Piaget spent his career attempting to explain the cognitive development of children. That is, how their intellectual level changes over time. He defined intelligence as a basic life process that is expressed by an animal's ability to adapt to its environment. The impetus for this cognitive development is a need to adapt to one's environment in order to survive, reproduce, live comfortably, etc. Piaget proposed that in order to grow intellectually, children develop increasingly more complex schemes, i.e. organized patterns of thought used to cope with or explain an experience (Shaffer, 2005).
According to Piaget, children are born without any knowledge. Children are constructivists, meaning that their cognitive development occurs because of curiosity and active interactions with the environment. Piaget found that children naturally and continuously organize schemes into specific hierarchies based on their knowledge of their environment. They then adapt to the demands of their environment by way of assimilation (understanding new experiences by incorporating them into existing schemes) and accommodation (process where children modify existing schemes in order to incorporate new experiences).
Piaget explained the course of cognitive development as being an invariant developmental sequence, meaning that each stage of development relies on the previous stage. The outcome of this process is a cognitively developed person. In a general sense, this outcome should be the same for the majority of individuals assuming the person was raised in an adequately stimulating environment. All children should go through the four stages of cognitive development, however people end up with differing schemes or understandings of their environment. This explains the multifarious opinions and thoughts we all have. Individual differences are a result of differing environmental influences. According to Piaget, children are constructivists, meaning that a differing environment will lead to differing scheme organization and therefore differing adaptation, assimilation,