If it's possible, go to school with him. Stay a little bit or all day, until he feels comfortable with your leaving him. pick him up after school until he's comfortable enough to ride the bus. Missing out of work or some dollars from your paycheck may be well worth it, over crying and worrying for days on end about it. If you work, explain to your boss what's going on. They should be understanding, if not, see about taking a week off to help your son get adjusted.

My son liked the bubble guppy episode about back to school. Have extra meetings with the teacher, and get then to have extra charts and graphs to communicate with him. See if they have extra staff incase if an episode of tantrums happen or get him to bring something that will calm him down back to a normal state. Weather it is from crying, being scared, afraid, or anger with my son having water on his face helps him calm down.

If the school will let you, take pictures of the door he'll enter, the door to his classroom, his locker or cubbie, etc. - in otherwords, all the places he'll go and things he'll see in the school, including personnel if they're O.K. with it.

Use the pictures to create a social story which carries him through his day. Then go over the story with him, and let him browse the book as often as he likes.

Picture books from the library, or videos like Caillou may be helpful, but if your child can't generalize from those stories to his situation, they can be confusing (things won't look the same, etc.)

We did like reuprict said and read lots of social stories, watched shows about going to school, discussed it frequently (dropped it into everyday conversations). Most importantly for us was to actually get him in the school building ahead of time. We're lucky in that Little Man's school has a couple of 'events' that they do each year before school starts (a hamburger fry fundraiser, a volunteer day, and before school conferences). These have become kind of like a ritual for him before school starts each year. This year we also asked his new teacher to meet us this week so that we can discuss his issues ahead of time without taking up the entire scheduled conference (they have specific items to cover then).

For us, repeated small exposures are the key.

Every year before school starts I take my son to school when its not in session , typically the week before and ask the teacher to meet us there with his schedule. This helps ease the anxiety a bit, once he sees the schedule he knows what his day will be like it helps ease him into the school year. Also any dvd's about going to school can help him see what happens in a class room. Social stories may help as well.