New school blues

[LauraPod]

We've just moved DS (7nearly8) and DD (5) to a new school, a wee school. DD is in P1 and has embraced the new life at the wee school, likes teacher, homework, other kids etc, DS is in P4 and is not engaging with new school well at all, is dwammy in lessons, easily upset, increasingly alone, finding it hard to join in with the already forged friendships of his classmates.
There are 50 kid in the school and it's an excellent place with great facilities and good ties between parents and staff, but DS is not enjoying it.
We're not over far from his previous school but we have left the ties there alone over the holidays in the hope that he wouldn't be harking back all the time to the great friends he has there and feel even sadder about leaving them behind. Now we've given him time to settle a bit and he hasn't linked up with other kids right off, we feel it's time to get back to playing with his old buddies, on playdates and days out and such. We would like him to keep his good friends, but not at the expense of making a good start at his new school.
Can anyone help me out with some tips on helping him to engage with the new school? It's only been a week and a bit since the school year started, but I want to see this situation improve, not deteriorate. Any suggestion?