What are the teachers doing about this bullying behavior on the part of the classmates? If they're allowing it to go on, then you have a bigger problem with the school than your DS not fitting in!
Why is your DS's age even an issue? Why do his classmates even know how old he is?
Have you arranged playdates with the older kids? Does he share interests with any of the kids that he could build on? Does he try to hang out with the most popular kids--who are most likely to reject him!--or does he attempt to make friends with the "fringe kids" who don't have a lot of friends themselves?
A lot of fitting in socially has to do with technique!
As for this:
So in our case we have learned that it is not good socially to skip grades.
No single solution is effective for every child. Some people do not do well socially with a grade skip, just as some kids do not do well socially without one. The more cliqueish the group of kids, the harder it will often be for a younger child to break in. But there are usually ways to improve the situation. Certainly the bullying should be addressed!
