Besides these extrinsic reasons, I consider two intrinsic reasons why this century-old system is still relatively prevalent and unchanged: alignment with findings from developmental and educational psychology, and breadth.

Montessori’s Convergence with Developmental Science: Self-Determination and Its Corollaries

Montessori was based in observations of children, which might explain why it dovetails very well with the accumulated evidence from developmental and educational psychology (Lillard 2017; Marshall 2017). Highlighting her intent to develop a system suited to human psychology, Montessori called her education system “Psycho-Pedagogy” (Montessori 1955/1989, p. 16), and the Italian title of her first book, The Montessori Method, was, literally translated, A Scientific Method of Pedagogy as Applied to Child Education in the Children’s Houses (Montessori 2012, p. 7). The generality and perpetuity of Montessori’s observations might stem from the variety of children and cultures in which she observed. Initially, Montessori observed atypically developing children, then children with extreme economic disadvantage, and eventually children on four continents from all social classes (Montessori 1962/1967). This variety of children could help render ideas that could apply to all children, even a century later. The central premise Montessori arrived at is that school should be “Help given in order that the human personality may achieve its independence” (Montessori 1955/1989, p. 6). After presenting evidential support for this central premise, evidence is presented on several features that can be viewed as natural corollaries to it. Many of these features are discussed at length in Lillard (2017).

Self-Determination

Independence means self-determination. Abundant theory and empirical evidence suggest the benefits of self-determination to the human psyche (Ryan and Deci 2000). Ryan and Deci claim that humans have three basic innate psychological needs: competence, autonomy, and relatedness. By setting children free in a natural social environment (meaning a place where they can freely interact with their peers) and providing conditions that cultivate sufficient social skills, relatedness is naturally achieved in Montessori settings (see “Peers” section below). By giving children opportunities to do many activities which children choose, and at the right level (difficult but not too challenging), a sense of competence arises (Cyvas 2010). And self-determination is of course at the very root of autonomy. Thus, the Montessori system is set up to satisfy basic human needs according to the self-determination theory.

Self-determination has several natural prerequisites and consequences, shown in Fig. 2 and detailed in the subsequent sections. To preview, self-determination requires that children choose their own activities. For free choice in school to lead to constructive learning, the activities must be interesting. Embodied and interconnected activities/knowledge engender more interest than purely abstract and disconnected ones. When deeply interested, we focus our attention, developing executive function. Extrinsic rewards undermine the sense of self-determination, so rewards must be intrinsic. A tightly ordered and organized environment and curriculum also facilitate self-determined learning. Self-determination allows for and, in fact, requires positive and caring teacher–child relationships, if teachers are going to have any influence. Finally, when children can determine their social groupings, they gravitate to arrangements that are satisfying for their age levels, and natural peer tutoring and collaboration can result. The evidence for each of these points is discussed below.

Fig. 2 Some evidence-based elements of the Montessori system Full size image

Free Choice

Montessori practice aligns with research in educational psychology by giving children considerable choice, which clearly confers a sense of self-determination. “The essential condition [for psychological health] is freedom to act in a prepared environment where the child can be intelligently active” (Montessori 1948a, p. 24). A great deal of evidence supports the benefits of free choice to well-being, learning, and development.

In one study, a group of children were asked to choose a category of anagrams to solve (Iyengar and Lepper 1999), whereas others were told their (yoked) category had been chosen for them. Students in the first group solved the most anagrams and were most likely to choose to take more anagrams home to solve on their own. In a second experiment, they found that even choosing the elements and names of objects in a computer game improved performance and task interest. In another study, babies who could move their own mobile by kicking their foot showed more positive affect, and later transferred their mobile-control knowledge to a new mobile; babies who could not control the initial mobile did not figure out that they could have controlled the subsequent one (Watson 1971). These and many other studies (for a review, see Lillard 2017, chapter 3) show that more self-determination, and the intrinsic sense or locus of control that goes with it, leads to more learning and higher well-being, across ages and settings, including school classrooms (Ames 1992; De Charms 1976). Findings are particularly strong when activities are interesting (Patall 2013), a Montessori feature discussed more below.

In Montessori classrooms, “children have free choice all day long. Life is based on choice, so they learn to make their own decisions. They must decide and choose for themselves all the time … They cannot learn through obedience to the commands of another” (Montessori 1989, p. 26). Montessori gained this insight from a simple incident in the first classroom in Rome (Montessori 1962/1967). The teacher had arrived late, to find that the children had asked the janitor to let them into school. At the time, the Montessori materials were kept locked in a cabinet until distributed to children by the teacher. Yet on that day, the children had taken the materials out themselves and were using them when the teacher arrived. Montessori was fascinated, and from that day, the materials were placed on low shelves and children chose their own activities.

Montessori noted that, “Children must develop themselves by their own exercises” (Montessori 2013, p. 22). She believed that intrinsic impulses cue the development sequence, and therefore, children’s development is self-driven (rather than adult-driven). She inferred that children have an internal drive to independence from watching babies learn to nurse, reach and grasp objects, sit, crawl, walk, and finally talk, essentially on their own, with no formal lessons from adults in these skills (Montessori 1967/1995). Until the late 1800s, this is how learning almost always occurred; only a tiny minority of the world’s children had formal schooling (Rogoff et al. 2001). Natural or informal learning “is nondidactic; is embedded in meaningful activity; builds on the learner’s initiative, interest, or choice (rather than resulting from external demands or requirements); and does not involve assessment external to the activity” (Rogoff et al. 2016, p. 358). In informal learning situations (versus in conventional school settings), children pay very close attention to the source of information; for example, a Mayan child learning to weave carefully studies the adult weaver (Rogoff 2004). In so doing, children act independently, taking control of their own learning by directing their attention. Montessori education is consistent with informal learning, and children learn in part by watching their peers (discussed later) and teacher demonstrations.

Montessori’s beliefs that (1) children have internal drives toward self-development, and (2) when unimpeded, development is healthy and normal, together imply that children are naturally driven to surmount challenges and to learn (see also Simon 2001; Vygotsky 1978), and will do so if given the right stimuli (for example, child-directed human speech) or tools (for example, objects to handle or climb on) and freedom to choose what stimuli to interact with, when, and how much. This is consistent with much educational theory (for further discussion, see Rathunde 2009) and evidence (“The Goldilocks Effect,” Kidd et al. 2012, 2014): Young children choose to attend to what is just above their current level—essentially in their “zone of proximal development” (Vygotsky 1978)—tailoring the input to facilitate their own development. Setting children free in an environment prepared to serve their developmental needs allows children to select stimuli from the environment to fill their proximate needs.

An analogy is found in the nutrition literature. In a classic study, 15 children were given a choice of 30 healthy foods each day from weaning until age 6, and their self-selected diets were nutritionally sound over long time scales (Davis 1928, 1939). More recent studies support this principle: At liberty among healthy choices, organisms select diets that meet their nutritional needs (Frankel et al. 2012; Johnson et al. 1991; Rovee-Collier et al. 1996). Montessori aims to provide an array of healthy choices for intellectual and socioemotional growth from which children can select what is needed for their current moment in development. In Montessori theory, two impediments to healthy self-development are (1) adults’ interfering with children’s choices, typically by providing extrinsic rewards or punishments, discussed later, or (2) adults failing to provide appropriate stimulators, leaving children bored.

Interesting Curricular Materials and Activities

Given free choice, children would only work with the materials and follow up on lessons on their own if doing so was interesting. Interest can be situational, as when most anyone would agree something is interesting, or individual, where a child has a particular intense interest (Renninger and Bachrach 2015). Regardless of which source interest has, research in educational psychology has made clear that learning improves when interest is aroused (Harackiewicz et al. 2016; Renninger and Hidi 2011). For example, children score more highly on reading comprehension items for topics they had previously noted were more interesting (Estes and Vaughan 1973; Renninger 1992). Adolescents’ advances on skills at which they had been identified as especially talented are predicted by how deeply interested the adolescents were at younger ages when engaging those skills, measured by experience sampling (Rathunde and Csikszentmihalyi 1993). And interest in reading is a strong predictor of later literacy (Whitehurst and Lonigan 1998).

Children in Montessori classrooms can choose activities and work on reports on topics that are personally interesting to them, giving a strong sense of self-determination. A child who loves frogs can make frogs the subject of art, math, biology, geography, and language endeavors. But self-determination is also helped by engendering situational interest. “The secret of success is found to lie in the right use of imagination in awakening interest, and the stimulation of seeds of interest already sown” (Montessori 1948a). Montessori materials and lessons were designed by trial and error to captivate children’s attention, and teachers are also trained to engender situational interest. “Whatever is presented to [a child] must be made beautiful and clear, striking the imagination” (Montessori 1948a, p. 17). Two supports to interest in Montessori are the work being embodied and interconnected.

Embodied Cognition

Montessori work is arguably interesting in part because it is embodied (Rathunde 2009); doing things tends to be more interesting than sitting still. Embodied or “grounded” (Barsalou 2008, 2010) cognition refers to the idea that thought is not composed purely of abstract, amodal symbols, but rather, is supported by the body (Wilson 2002), and in some cases even offloaded to the body and the external world (Byrge et al. 2014; Clark 2013; Pouw et al. 2014a, b). It includes the idea that metaphors reflect how our bodies are constructed and function (Lakoff and Johnson 1999) and systems perspectives in which organisms develop in dynamic interplay with their environment (Smith and Thelen 2003).

Abundant evidence supports that learning and development are helped when they are embodied (but see Pouw et al. 2014a, b). As evidence, consider that infants who manually explore objects have more advanced visual perception regarding objects (Needham 2000). Handling objects also predicts understanding others’ reaching behavior to be goal-directed, and infants who are given early experience handling objects (by giving pregrasping infants “sticky” Velcro mittens that attach to cloth toys) appreciate others’ goals earlier (Sommerville et al. 2005). With older children, movement has been shown to enhance memory, literacy, and physics understanding. For example, motioning one’s hands as if to pour enables better prediction of the angle at which water would pour (Schwartz and Black 1999) and walking in various positions on a carousel allows children to understand that all parts of an object move at the same speed better than does watching the carousel (Levin et al. 1990). Children who trace letters while making the associated sounds learn sound–letter relations better than children who look at letters while making sounds (Bara et al. 2007), and the act of writing enhances reading skills (James 2017). Many more studies support embodied cognition, explaining its current prominence in discussions of schooling (de Silva Joyce and Feez 2018).

Piaget, who took Montessori’s training course and was president of the Swiss Montessori Society (Baumann 1999), noted Montessori’s prescient recognition that cognition is embodied: “Generalizing her discoveries with unparalleled mastery, Mme Montessori . . . immediately applied to normal children what she had learned from backward ones: during its earliest stages the child learns more by action than through thought [, leading her to develop] a general method whose repercussions throughout the entire world have been incalculable” (Piaget 1970, pp. 147–148). Montessori’s books are replete with quotations expressing the connection she saw between movement and cognition, for example: “Watching a child makes it obvious that the development of his mind comes about through his movements… Mind and movement are parts of the same entity” (Montessori 1967/1995, p. 142). Montessori is deeply concerned with educating children’s movements, and it uses movement to teach (Rathunde 2009).

Feez (2018) provided an example from geometry. The youngest children in a Montessori primary (3 to 6) classroom are taught to fold cloths they will use as napkins or for cleaning. Lines are sewn in the cloths to show children where to fold them, resulting in squares, rectangles, and triangles. Children learn the names of these shapes, and later come to apply them to other material, including a language material called the metal insets, a set of 10 geometric shapes which children trace and eventually use to make Spirograph-like artistic designs (see Montessori 1934/2011). When children trace the metal insets, they learn names like pentagon and ellipsoid, which they will apply in later geometry work and elsewhere. By tracing the metal insets with pencils, children also receive indirect preparation for writing. They also trace many more additional shapes in a geometry cabinet; here they trace the shapes with their fingers while saying the name, continuing preparation for writing. A puzzle-like game in which the wooden pieces are placed on cards showing the shapes’ outlines ensues, and is a step in a movement toward abstraction, as the cards become symbols, as do the words, and children eventually leave behind the tracing and can simply use the word to denote the concept. Some of the geometric shapes resurface as children learn parts of speech, with a black equilateral triangle representing the noun family and a red circle representing the verb. Children place these symbols (and others representing other parts of speech) next to words as they diagram sentences. “By combining objects and movement with language in multimodal ensembles of learning resources, Montessori designed sign complexes in which sensory and intellectual meanings are unified. These ensembles isolate and give prominence to the critical variables and contrasts from which educational knowledge emerges” (Feez 2018, p. 45).

Also related to embodiment, Montessori is well known for its encouragement of fine motor skills; even in conventional kindergartens, Montessori exercises significantly strengthened such skills over 6 months (Rule and Stewart 2002). Control of one's hands is related to intelligence more generally (Deary et al. 2004; Melnick et al. 2013), and children’s fine motor skills strongly predict later school success (Cameron et al. 2012; Grissmer et al. 2010).

Interconnection

People also tend to be more interested in material that connects with other material they already know in part, but not thoroughly (Berlyne 1960; Hidi and Renninger 2006; Tobias 1994). Hence, an excellent study strategy is “bridging”: thinking about how new material connects to other materials one already knows (Miyatsu et al. 2018). “Advance organizers” like outlines also serve this function by giving people concepts on which to anchor new information (Mayer 2008). The Montessori system capitalizes on bridging. “It is well-known that … [one must link] all new knowledge to the old, ‘going from the known to the unknown,’ because what is absolutely new can awake no interest” (Montessori 1917/1965, p. 45). Throughout the Montessori curriculum, from birth to high school, there is a great deal of interconnection; the napkin-folding-to-grammar symbol sequence just described is one of many. At the elementary (6 to 12) level, interconnection is explicit in the title: Cosmic Education: Children are presented with the universe as an interconnected entity. “All animals and vegetables [even] insects have a cosmic task. All are agents, maintainers and conservers of this order in the environment” (Montessori 2012, p. 89).

Self-determination requires that activities be interesting, and embodiment and interconnection are two ways to make them be. A consequence of engaging in activities in which one is very interested is that attention becomes fixed and deeply concentrated. This is another way that Montessori is aligned with educational psychology research, which could account for its persistence.

Concentrated Attention

When one is deeply interested in one’s task, one concentrates deeply, engaging full attention (Csikszentmihalyi 1990). The ability to control attention is a highly laudable goal for education (James 1890, p. 424). Attention is a pillar of the executive system (Petersen and Posner 2012), which has been tied to school and life success (Blair and Raver 2015). For example, self-regulation at ages 3 to 6 predicted age 32 health, wealth, and criminality outcomes in a sample of over 1000 people born in 1972–1973 in Dunedin, New Zealand (Moffitt et al. 2011).

Deep-focused attention is central to Montessori education. “The task of education is to fix the wandering mind of the child” (Montessori 1994, p. 105). Once children began to concentrate on self-determined work, Montessori said, “The child’s whole personality changed, and the first sign of this was an assertion of independence. It was as though [the child] were saying: ‘I want to do everything myself’” (Montessori 1967/1995, p. 130). Thus, concentration appeared to enable self-determination. In addition, several other positive characteristics were said to emerge once children began to concentrate on work: they became joyful, empathetic, kind, and respectful of others, began to make good choices, became more compliant, perseverant and so on (e.g., Montessori 1962/1967, 1966, 1967/1995). Research does indicate that Montessori particularly develops executive function (Diamond and Lee 2011; Kayılı 2018; Lillard 2012; Lillard and Else-Quest 2006; Lillard et al. 2017). The characteristics Montessori noted also resemble the “autotelic” personality associated with regularly achieving “flow” states through deep concentration on work (Csikszentmihalyi 1997) and characteristics of a self-regulated learner (Blair and Raver 2015). Such effects of concentration have even been observed in monkeys: Nonhuman primates raised in captivity, natural models for attention deficit hyperactivity disorder (ADHD), improve in their behavior following training on how to use a joystick, a task requiring their sustained attention (Rumbaugh and Washburn 1996).

In sum, self-determination requires interesting activities, which lead to deep attention, promoting executive function—another way in which Montessori education is aligned with research findings. And executive function in turn supports healthy choices in a context of self-determination. Self-determination also requires that one avoids extrinsic rewards, like gold stars, grades, and “reading for pizza” programs, because research shows that such rewards negate a sense of self-determination (Deci et al. 2001).

All Rewards Are Intrinsic

Besides requiring interesting activities, environments marked by self-determination lack extrinsic rewards, praise, and overt evaluation that can be taken as means of extrinsic control—an “overjustification effect” (Lepper and Henderlong 2000). Consistent with its goal of self-determination, Montessori also lacks these elements. There are no grades, and teachers are counseled not to praise or openly evaluate children (except if a child clearly seeks praise, see Montessori 1967/1995). The materials are self-correcting, and children learn to find their own errors using control materials. Montessori believed that children naturally want to fix their errors, in keeping with a natural tendency to virtuosity (Kubovy 1999), but that “All the crosses made by the teacher on the child’s written work. .. only have a lowering effect on his energies and interests” (Montessori 1967/1995, p. 245).

There is considerable controversy about the long-held practice of extrinsic rewards in school, which Thorndike over 100 years ago urged on teachers-- to reward correct associations with candy and pats on the head and to punish incorrect ones with “stern looks” (Jonich 1962), and extrinsic reewards are embedded in the conventional model. Although there are likely many reasons why children’s intrinsic motivation to learn in conventional school declines every year they are in school, research suggests extrinsic rewards might be one. And intrinsic motivation is positively related to school performance, whereas extrinsic motivation is negatively related (Corpus and Wormington 2014; Lepper et al. 2005). An ample body of research has shown that if people are already motivated to engage in an activity (as perhaps young children are in school learning), using extrinsic rewards depletes motivation once the rewards are removed (Deci et al. 1999). Extrinsic rewards are detrimental in part because they create a sense that other people are responsible for one’s outcomes—in other words, they undermine the sense of self-determination (Deci and Ryan 2011). Montessori’s lack of grades and other extrinsic rewards is another way in which it is aligned with educational psychology research (see Lillard 2017, chapter 6).

Natural Peer Engagement

Self-determination applies not only to activities, but also to social milieu: Children are free to choose their social arrangements in Montessori classrooms. This has led some to claim Montessori is asocial, because rather than all acting together as a single group, as they do when teachers lead whole-class activities, children (especially before age 6) often engage in different individual activities, although they might be working side by side (even on the same type of activity) and conversing. Another way children in Montessori classrooms commonly interact is peer tutoring, with older children helping younger ones (Montessori 1967/1995). At the elementary level (ages 6–12), children in Montessori classrooms almost constantly engage with others, collaborating on reports, deciding on the nature of their report, how to conduct the research, who will do what parts, how it will be presented to the class, and so on. Educational psychology research on peer and collaborative learning supports this natural Montessori sequencing of more individual work at younger ages transitioning to more group work with age (Hartup 1983). Research also supports the efficacy of peer tutoring and collaborative learning.

For example, low-SES children who were assigned to engage in a peer tutoring program significantly outperformed those who did not, not only in the topic tutored but in all other topics and even 2 years after the tutoring program had stopped; they also performed as well as a higher SES group (Greenwood et al. 1989). Collaborative learning programs like Brown’s “Communities of Learners” and Jigsaw Classrooms are also very successful (Aronson and Patnoe 1997; Brown and Palincsar 1989; Rogoff et al. 2001). Yet children’s skill and proclivity toward peer interaction increases with age (Hartup 1983), such that the benefits of collaborative learning manifest after age 6 (Azmitia 1996) except in special in laboratory situations where they have manifested at 5 but not earlier (Plötner et al. 2015). Typically, “Even 5-year-olds, competent problem solvers in many instances, have difficulty working together to solve any but the simplest and most familiar problems” (Siegler 1998, p. 277). In addition, as children get older, their desire to be with peers increases (Hartup 1983), and working with peers enhances interest (Renninger and Hidi 2011; Thoman et al. 2012). Self-determination in Montessori classrooms appears to allow children to gravitate toward the social arrangements that correspond to their developmental capabilities and proclivities (see Lillard 2017, chapter 7).

Warm and Supportive Teacher–Child Relationships

For teachers to influence development when children are free to make their own choices, positive teacher–child relations are especially important (Davis 2003; Pianta 1997). Montessori presaged current research by focusing on the importance of teacher–child relationships (Whitescarver and Cossentino 2007). She counseled teachers on exactly how to behave with children, in ways consistent with secure-attachment parenting (sensitively responsive) and authoritative parenting (adults provide guidance, but give children considerable autonomy within those strict boundaries; see Lillard 2017, chapter 9). For example, she said, “Young people must have enough freedom to allow them to act on individual initiative. But in order that individual action should be free and useful at the same time it must be restricted within certain limits and rules that give the necessary guidance” (Montessori 1948b, p. 113), and “A teacher [must be] ready to be there whenever she is called in order to attest to her love and confidence” (Montessori 1956, p. 76). Life outcomes are better when children are securely attached to warm and sensitive caregivers (Drake et al. 2014; Stams et al. 2002) who become authoritative as children grow up (Baumrind 1989). The importance of warm, sensitive, responsive teachers who can build positive relationships is clear; teacher–child relationship quality predicts child outcomes (Pakarinen et al. 2017; Pianta et al. 2002). Montessori was at the vanguard in seeing the importance of such relationships for human learning. Presaging Baumrind’s (1989) description of the authoritative parent, she wrote, “It is true that the child develops in his environment through activity itself, but he needs material means, guidance and an indispensable understanding. It is the adult who provides these necessities… If [the adult] does less than is necessary, the child cannot act meaningfully, and if he does more than is necessary, he imposes himself upon the child, extinguishing [the child’s] creative impulses” (Montessori 1956, p. 154). To the extent that Montessori’s recommendation for how teachers relate to children holds true, this is another way in which Montessori adheres to research in developmental science.

Orderly, Organized Environments

Another aid to the success of a self-determined learning environment is organization. Abundant research has shown that children thrive when conditions are orderly and predictable. In one such study, kindergartners received over 2 weeks six lessons in a nearby classroom; for three lessons, its walls were filled with decorations and information, as one often sees in classrooms (Bullard 2013); for the three other lessons, the walls were sparse, containing just a little information relevant to the lesson. Children’s attention was coded during each science lesson, and their learning was tested after. The results suggested that children were distracted by the cluttered walls: They spent more time looking at them than the teacher, and they also learned significantly less. This experimental study is consistent with a naturalistic study in the UK of over 3500 children, ages 3 to 11, in 153 classrooms in 27 different schools (Barrett et al. 2015). Across the school year, children learned the most in classrooms in which walls provided an intermediate level of stimulation, “in balance with a degree of order, ideally without clutter” (p. 129). Other studies have examined household chaos and clutter: children who grow up in homes with more structure and order (temporal and spatial) fare better at all ages, even controlling for demographic third variables like SES (Evans 2006). Other studies have focused on routines, from bedtime to chores to holidays, and again, have found that children thrive on order (see Lillard 2017, chapter 10).

As described in Montessori’s books, an authentic Montessori classroom is a modicum of order both at the macro level and micro levels, and in physical and temporal ways. For example, the classroom is prepared in an orderly fashion, with like materials together, so there is a math area, a language area, and so on. In addition, within and across sets of materials, factors like color are held constant. All the items on the “table washing” activity tray will be the same shade of blue, for example; and across all the decimal math materials, units are green, tens are blue, and hundreds are red; this sequence repeats for the thousands. There are set sequences with which to use all the materials, and set ways to remove them from the shelves to which they are returned by the child after use, all in order. In addition, the object of many of the materials—the game so to speak—is to put things in order. One messes up then arranges the color tablets, for example, from lightest to darkest, or places all the like pairs together. The classrooms have auditory order as well, as children are taught to use calm voices like their teacher uses. “Pedagogically the work of the school is to organize the work of the child …The organizing of the child’s work and offering this work to the child is a very exact work for us… It is the organization of the work which [leads to]… the establishment of mental order” (Montessori 1997, pp. 31–33).

Montessori’s organized approach to sensorial education provides another example that is pertinent to developmental neuroscience. In the late 1800s, Wundt’s laboratory in Leipzig was interested in the limits of human perception, while Montessori was interested in how to aid human perception. As noted earlier, the ability to make fine sensory discriminations is correlated with intelligence (Deary et al. 2004; Melnick et al. 2013). Brains are hierarchically organized, with lower levels feeding into higher ones (Merzenich 2001; Stiles et al. 2015). Montessori’s theory was that by presenting children orderly, graded arrangements of sensorial impressions—light to dark shades, lower to higher notes, rough to smooth boards, and so on—the haphazard impressions of real world stimuli would have an organized neural system in which to be registered. Given that we know the sensory cortex is organized in this (tonotopic, etc.) fashion (Hari et al. 1993; Merzenich 2001; Romani et al. 1982), and that neuroplasticity is specific to the input (Lillard and Erisir 2011), Montessori’s ideas make sense. Furthermore, given the hierarchical nature of neural organization, it is possible that organization at the lower sensory levels feed into organization at the higher levels (Lillard 2017).

Order might explain the discrepancy between poor outcomes from pure “discovery learning” approaches (Klahr and Nigam 2004; Mayer 2004) and better outcomes from “guided play” approaches (Alfieri et al. 2010; Verdine et al. 2017). In Montessori classrooms, children are not simply let loose with stuff to do as they please. They are given orderly lessons with how to use each material; everything is tightly organized with prescribed procedures of use. Sometimes lessons are given by peers rather than the teacher, and peer tutoring is most effective when procedures are tightly structured (Fantuzzo et al. 1992; Ginsburg-Block et al. 2006). Thus, the order of the Montessori environment also supports its guiding principle of self-determination.

Summary: Self-Determination, Its Corollaries, and Montessori’s Alignment with Educational Psychology Research

In sum, Montessori is well-aligned with educational psychology research. Its central premise of self-determination can be seen as the core from which several other alignments follow. Self-determination necessitates free choice, which is helped by not having extrinsic rewards that can be perceived as manipulative. If children are to have free choice in school and still learn, it requires that the learning activities be very interesting, so children will want to do them. Interestingness in Montessori work is helped by its being embodied and interconnected. The degree of interest also inspires deep attention, which develops executive function, that then assists self-determination. Self-determination also requires positive warm teacher relations, in order for teachers to have influence at times when children need their subtle guidance (subtle to retain the sense of self-determination). Free choice also allows children to adopt social arrangements corresponding to their levels of social development. Finally, constructive development in a self-determined environment is likely helped by the environment being tightly organized. Montessori arrived at these principles through close observation of children, and education and psychology research today support the conclusions to which she came. This alignment with research could be one reason Montessori is so admired, and hence, continues to exist so long after its development.

Montessori’s Broad Scope

Besides its good outcomes and its alignment with psychological research, another appeal of Montessori its broad scope, three facets of which are discussed here.

Age

The basic tenet of Montessori—to set children free in a prepared environment, in which they will self-educate—applies at all ages. Children become increasingly independent of adults across the schooling years, but the basic Montessori method remains the same across them. Montessori noted that, “Other methods have not so wide a function” (Montessori 1955/1989, p. 5) in the ages served: Froebel’s kindergarten and Reggio Emilia were designed for children under age 7; Pestalozzi and Steiner developed schools for children ages 7–12; the Dalton Plan was developed for high school; and so on. Montessori serves a broad age range, from birth to 18, which could be part of its appeal and longevity.

Global Reach

Montessori education was intended not for children in a single particular culture but for a biological human being. Children everywhere adapt to their cultures; Montessori is designed to give children “a knowledge of the environment to which [they] need to adapt [themselves]” (Montessori 1955/1989, p. 11). Montessori schools are in at least 110 (Whitescarver and Cossentino 2008) of the world’s 195 countries, from China to Argentina, Australia to Finland, Kenya to Malaysia, and even (as I have seen) in the tiny Himalayan Buddhist Kingdom of Bhutan. The differences in Montessori across countries lie in culturally specific symbol systems (sandpaper Chinese characters, for example), practical life exercises (making sand mandalas versus polishing shoes), whether materials are purchased or handmade (as they are in less affluent countries), and basic elements like classroom density (higher in densely populated cities like Mumbai). In other respects, Montessori classrooms enact the same basic curriculum with the same materials around the globe.

Intraindividual Development

In addition to being broad in ages served and cultures in which it has integrated, Montessori education covers a broad range of areas of development (Montessori 2012). The Montessori system began with children ages 3 to 6. Children begin learning in this classroom in two areas: practical life and sensorial. The former educates children on how to take care of themselves and their worlds: how to get along with others (with “lessons of grace and courtesy”), and prepare meals, set the table, and clean dishes, arrange flowers, mop the floor, and so on. In these latter activities, the hand works in service of the mind, and many children have their first moments of deep concentration in the classroom while doing such work; others experience those moments in sensorial work (Montessori 2012). As noted earlier, sensorial activities systematically educate the senses by having children pair like objects (for example, musical bells of the same pitch) and arrange objects in order (lowest to highest pitch). The array of sensorial discriminations made includes colors, textures, temperatures, weights, sizes, shapes, smells, tastes, and so on. Stemming from the sensorial training, Montessori presents materials that lead children to discover how to write and then read, as well as how to do mathematics and geometry. Children are also introduced to the continents and countries of the world (including their geology and biology) and given vocabulary to describe the universe and its contents. In sum, the curriculum in a Montessori primary classroom is intentionally broad, carefully constructed to assist the child’s whole development, from social skills to mathematics.

A similar approach was taken in bringing the method down to infancy (Montessori 1967/1995). For example, infants are initially given mobiles with specific patterns to help to develop the visual cortex (black–white contrasts in the earliest mobiles, gradations of color in later ones). Later they are given interesting objects to interact with, often just outside of their reach, to inspire them to move toward the objects, purportedly to develop a sense of agency. Children are given limited choices initially, which increase as they become able to handle choices.

In elementary, for ages 6 to 12, the Montessori curriculum enlarges to embrace the entire cosmos (Montessori 1948b). Montessori found that this scope engages children from age 6 on; less scope, she said, kills interest. “If neglected during this period, or frustrated in its vital needs, the mind of the child becomes artificially dulled, henceforth resistant to imparted knowledge” (Montessori 1948a, p. 3). In middle and high school, children in Montessori become increasingly independent, increasingly moving into and interacting with the real world, while continuing to make interconnections and learn in collaboration with peers. Montessori’s idea was that from 12 to 15, children engage in practical work using what they have already learned; they might live on a farm, take care of animals, build farm structures, and run several businesses associated with farm products, run a hotel, and so on. From 15 to 18, school becomes like university.

In sum, Montessori education is unique in its broad scope with regard to the ranges of ages and cultures served, topic areas covered, and aspects of development it aims to foster.

Summary

Montessori education exists basically unchanged over 100 years after its founding. I have reviewed three extrinsic (outcomes, teacher satisfaction, and alignment with parent goals) and two intrinsic aspects of Montessori education (alignment with developmental science and breadth) that might explain why. And yet Montessori also remains on the margins (Whitescarver and Cossentino 2008) and is often ignored in discussions of school reform (Dintersmith 2018). In the next section, I explore possible reasons why this is so.