I can think of a reason...Free "childcare" during the school hours means "free" time for Mom. Plus, the school is on the hook to pay for all the therapies and special high tech learning aids he needs that may cost thousands of dollars. Mom doesn't even have to find a ride or use her gas to take him to appointments, because they do most therapies at school. Medicaid picks up a lot of the costs, also. Maybe he qualifies for the meals program, and the cost for a tech to sit with him all day. No way Mom could afford all of that.
Educators out there... tell me if I am wrong.