Debbie,
Welcome home!
You go to the school. If you just sit quietly he will likely calm down eventually. Or go to a different room with kids of the same grade - it's them you've come to see, not really your own - you know your own pretty well by now.
You wanna feel the lack of stimulation first hand - that'll help put things in perspective. It's not that schools are bad. It's that normal development is normal, and different than DS's. You wouldn't ask any of those normal kids to go back and repeat their previous year of school to develop their social skills - you just wouldn't!
You're so good. Horray for you for stepping out of line!
Trinity
