I agree with the previous responders... your son is probably having a hard time adjusting and acting out is his way of handling his emotions. That is a lot of change for him. If he was still in the old daycare and starting the new school, he may find comfort knowing he's going to see the "usual crowd" after school and not be so anxious. I'd have playdates as often as possible. From the old and new daycare as well as school. Reinforce with him how wonderful it is to make new friends and keep old ones. The playdates don't have to be expensive or extra work for you. Maybe arrange a meeting at the playground for a bunch of kids. You could bring a snack for them to share. Or see if people are up for going to Chuck E Cheeses or some similar type place.
The teachers are bound to have some helpful advice too. Try to keep an open mind and know that they are handling more than just your kid and they want everyone to thrive. Perhaps you can ask the teacher if she has special chores for kids to do... wipe the desks, manage pushing in the chairs, wiping the blackboard, etc. Kids love to have duties that make them feel important. Maybe your child needs to have some duties (however small they may be) to feel like he is an important part of this class too.
I wonder if the other kids know each other? Have they had years of history together (like your son did in his previous situation) and that makes them harder to approach. Maybe his teacher will let him bring in some special napkins to share at lunch with spiderman or something else cool on them. That is a low cost way to make him feel like a special kid.
Good luck. I always feel horrible for kids who have trouble adjusting. You want so badly for them to feel happy and confident. He probably just needs a little extra assistance and then he'll find his comfort and do great.
Take care,
Liz