The Least Restrictive Environment was designed to level the playing field. This goes back to the reason why we have Special Education in the first place.
There was a time when there were an inordinate amount of blacks represented in Mentally Retarded (MR) classes, and/or the kids in Special Education were treated as second class citizens.
This basically says that the child has to be educated in the place where he/she will gain the most benefit. They shouldn’t be put in classes far away from other children just because they are in special education.
Here is the website that will explain more: http://sped.lausd.net/sepg2s/pg2_lre.htm