I think he just needs adjustment time. We as the grown-ups know that this kind of change will be fine, but for a kid it can be a much bigger deal. The best you can do is some of the things you've already done. Then just be a role model for him. Give him a big, reassuring kiss and hug good-bye, smile as you leave and let the teachers handle the tears. If you're stressed about it, he's more likely to be stressed about it. So many kids cry at the beginning of the school year (sometimes for days, weeks or longer!), but they adjust. It just takes time. He'll be fine and so will you! :)