Well, due to his delays, whatever they are, he would be evaluated and given an IEP (since he's over 3) for whatever services he is eligible for: speech, PT, OT, Bx, etc. Not sure about Arkansas, but in FL he'd be evaluated by his local school board and could qualify for part-time or full-time at the elementary school he is zoned for. If he were under 3, his eval would be through a early intervention organization and go from there. Had he started in early head start, he could have "graduated" from services by kindergarten if he responded well.
Yes, we do for children with special needs, but in general, children should be potty trained by the time they enter regular head start. Those classrooms aren't equipped to change diapers. Early head start classrooms are working on potty training.