I would say give it a month or so, just to see how the school handles DS on their own. I have seen really awful teachers, and really amazing ones. DD's first grade teacher this year is by far the best that either of my kids have had. I was worried, because the teacher is so young, and I assumed, inexperienced. But she differentiates EVERYTHING, (don't ask me how she manages that, with 24 kids in the class), looks up special spelling words for DD, since she is far ahead of the rest of the class in reading and writing, and even put together a special section on poetry just for her - because she was interested in it. On the other hand, DS had a teacher last year who seriously told me that the class should not adjust for him - he should adjust for the rest of the class. She used the spiderman argument - "with great power comes great responsibility." In her mind, if he was ahead, he needed to spend his time helping others (not that I have a problem with him helping, but I didn't think that was much of a challenge for him). Anyway, I'm on a tangent. My point is, build a relationship with the teacher. As soon as you know the teacher's name, shoot him/her an email explaining that you don't want to start off on the wrong foot or sound pushy, but these are DS's strengths AND weaknesses. Be careful - don't EVER use the word "bored" with a teacher. But make it clear that you are concerned about challenging your child, and you are willing to help with that however you can. (Teachers tend to be more likely to listen if they know the parents are involved, and they are not expected to work miracles on their own). After that, watch the assignments coming home and evaluate for yourself. Don't be afraid to contact the teacher frequently - as a former teacher, I can tell you that almost anyone who works with kids would rather deal with a parent who contacts them frequently than one who ignores the problem until it is almost overwhelming. With DS and his horrible teacher, I started keeping a file of sample work he had done at home, so I could take it in and show it to her - so she knew I was not just making it up or exaggerating his abilities.
Above all, give the teacher a chance. If she doesn't do what you think is appropriate for your child, by all means talk to administrators, counselors, AIG coordinators, or whoever else you think would be helpful. But deal directly with her first.
Good luck!