The text of the IDEA defines the goal of LRE in somewhat labored prose, as:
To the maximum extent appropriate, children with disabilities, including children in public or private institutions or other care facilities, are educated with children who are not disabled, and special classes, separate schooling, or other removal of children with disabilities from the regular educational environment occurs only when the nature or severity of the disability of a child is such that education in regular classes with the use of supplementary aids and services cannot be achieved satisfactorily.
A simpler way of looking at LRE, and one that has been adopted by the New York City Department of Education, among others, is to think about a continuum. One end of this spectrum would be educating children in their neighborhood schools in a regular class without any special supports. That would be the least restrictive setting possible. Next, and somewhat more restrictive, would be educating children in regular classes with specialized supports. This could include providing accommodations or curriculum modifications to a particular child in the regular class, or having a para-professional come into the regular classroom to assist a student. To the extent that a student is "pulled out" of the classroom for some or all of the day, for services like speech and language therapy or resource room, that would be more restrictive, but still within the confines of a regular class most of the time.
Further away from the least restrictive end of the continuum would be a self-contained class in a regular school, followed by a specialized school. On the most restrictive end of this continuum would be residential schools for children with the most significant disabilities, who cannot be served in any less restrictive setting. As the New York City Department of Education notes, any move away from a general education class should be considered only if a "child would not be able to make meaningful progress in a general education class, even with the help of supports and services."
Why is this important? Being in a regular class offers children with learning and other challenges the opportunity to make friends in their neighborhood and to improve behavior, communication, academic, and social skills. Typically learning children benefit as well; they gain in social and emotional growth and in their understanding and acceptance of diversity. Classes where typical learners are educated alongside students with learning challenges, with the addition of a special education teacher in the room (sometimes called Collaborative Team Teaching) is one way significant numbers of students are getting the benefits of these opportunities.
Not every child will do well in a general education setting, and many children only begin to thrive when they are in a more restrictive setting where they can improve both their academic skills and confidence. But all parents should understand the goals of LRE and consider how they may apply to their own child's educational setting.