Centers are quite common in Kindergarten and 1st grade. They are suppose to teach and promote working independently, which is important for the older grades. Students might spend 20 minutes reading quietly in one center and then move to science center where the kids might work together to figure out a science problem.
I assure you the other kids aren't teaching your son. The group work is suppose to promote communication between peers.
EVERYTHING that is re-enforced during centers is formal taught by the teacher first. For example, in a kindergarten writing center, the students might have to practice writing A's and B's. Well, the teacher has formal taught this before.
Your child seems to be having difficult adjusting, which is causing problems. Kids should know what centers they are in w/o having to ask the teacher. Even if it's the first week, he should be able to know what group he's in (like group A or group b) At 6 years old, kids should be able to remember that quickly. The teacher isn't going to tell your son everyday what group he's in. Part of school is teaching kids to function independently. If she keeps telling him what to do (like the direction to worksheets, when he has the ability to read) , she is contributing to his inability to reason and do for himself.
Also, since your son is VERY new; she might be feeling out his academic level. Some kids have a difficult time adjusting, so they "act" like they don't know how to do something. The teacher wantst to see what you son KNOWS on his own. If the teacher reads your child the directions, shows him what to do or explains to him a lesson; she can't get a real idea of where he is academically.
More then likely, she is trying to figure out what your son knows or is capable of doing (academically and socially) before she gets involved. This is a smart move on her part. Your son has only been in her class for 5 days and is completely new to a mainstreamed school environment. She is well aware that she can't make sound conclusions on your son's academic level in such a sort amount of time and considering the circumstances.