Autistic support classrooms have several great advantages: they are usually very small, with a high adult to child ratio. They offer supports, such as visual teaching tools, which are specifically selected for autistic students. And they may also include intensive speech and social skills training in their curricula. In addition, children in autistic support classrooms, like those in special education classrooms, are usually included in general school activities such as assemblies, recess, and so forth.
Autistic support classrooms, however, tend to be quite segregated from the rest of the school. Children in these classes often spend all or most of the day with other autistic children. In addition, with so much attention paid to building social skills, these classrooms may neglect your child's academic strengths and abilities. It's not unusual for teachers of children with autism have lowered expectations of their students' intellectual abilities.
Resources:
Department of Elementary and Secondary Education. Questions and answers about no child left behind: update 2004.
Hayes, N. To accommodate, to modify, and to know the difference: determining placement of a child in special education or A504. New Horizons for Learning, 2000.
Iovannone, R., Dunlap, G., Huber, H., & Kincaid, D. Effective educational practices for students with autism spectrum disorders. Focus on autism & other developmental disabilities, 18(3), 150-166 2003.

