An article from Disability Scoop, "Study: Inclusion May Not Be Best After All" by Michelle Diament, 11/1/11, summarizes an article from the journal Pediatrics . The study involved almost 500 autistic students and compared those who had spent 75 to 100% of the time in regular classrooms with those who were in more segregated settings. Those in inclusive settings were no more likely to complete high school, go to college or see improvements in cognitive functioning.
“We find no systematic indication that the level of inclusivity improves key future outcomes,” researchers from the University of Alabama at Birmingham and Johns Hopkins University wrote.
The Disability Scoop article goes on to misleadingly state that the Individuals with Disabilities Education Act requires that special education students be served in the "least restrictive environment"(LRE) meaning in regular classrooms. This is what most advocates for inclusion will tell you, but it's not true and it never has been true. The LRE is part of the placement decision and is based on the needs of the individual student.
Beyond the outcomes that were investigated in this study, there are all kinds of reasons to place children in inclusive settings or to opt for more segregated settings. The problem is that Inclusion fanatics have for years asserted that placing all children in regular classrooms with their non-disabled peers is better in all respects for everyone involved. But then Inclusion fanatics have always existed in a fantasy land undisturbed by reason or evidence.
Be sure to read the excellent comments on the Disability Scoop article.