I don't know if this is going to be helpful, KMG, since I haven't had direct experience of this problem, but my 8 year old son has been to three nurseries and three primary schools and so he's been the 'new boy' more often than we'd like.
Even though he was and is sociable, I can't say that he made many good friends at nursery. He was rather boisterous, so this probably put off the quieter children. He used to play happily in groups, but we never got into the meeting up in the park, invitations back to tea routine. But then I was working, so I wasn't there to pick him up, chat to other parents, issue invitations etc.
He made more friends at his schools - I think children do form more lasting friendships then, anyway, as they get past five years. Also in my son's case, any tendency to aggression slowly abated from age five as well, so he didn't get labeled as a bully, despite my previous fears.
Hopefully, you might find this too. Also, IME, classes vary - just the personal chemistry of 30 or so children could make one set of classmates seem more friendly to your son. My son definitely found one of his schools more friendly than the other. Hopefully you'll strike lucky with your son's new school.
I think there's quite a lot you can do to help your son make friends. As already suggested, have a word with his class teacher. They might pair up your son with another child who will show him the ropes. This happened to my son on two occasions and it really helped him settle in.
Also, be proactive in getting to know the other children and parents. More easy if you are there to take and collect him, but not impossible if you don't have daily contact with the school - school events crop up with great regularity. I get my son to tell me who he's played with, point them out to me, show me the parents, then I'll introduce myself, and if all is going well, at some point I'll suggest their child comes round to tea etc. It took me ages to get into the swing of this, by the way! Having a fledgling friend round to tea helps me see how my son behaves with them as well. Also, your son is old enough to join different clubs and activities so you and he can meet his classmates outside school.
Anyway, hope these suggestions help. IME friendships do form more easily at school than at nursery. Hope the same is true for your son.