Least Resrictive Environment (LRE) is, simply put, the place where a student with a disability has their needs being adequately met and is with their non-disabled classmates, family, and community as much as possible. While for many children this place is in the general education classroom where the regular classroom teacher is able to provide an intervention so their education is not impeded, for other children with special education needs, this place may be in a general education classroom part time and a special education resource room the rest of the time or a classroom that is co-taught by the regular and special education teacher. The child's educational needs must always be satisfactorily met, and they must have the support they, as an individual, need in order for them to be in their LRE. If they are being rejected by their peers in a general education classroom, their learning is most likely being impeded and for them, this is not their LRE. So, while the general education classroom may often be a student's with special education needs LRE, it doesn't have to be.
References:
Hallahan, D., Kauffman, J., & Pullen, P. (2013). Current Practices for Meeting the Needs of Exceptional Learners. In Exceptional Learners: An Introduction to Special Education (Thirteenth ed., pp. ). Pearson.