I was told by another parent that if a kid has an IEP the parent can request a certain teacher. Last year DS just had an IEP for speech articulation so I really didn't think that any requests I made would be taken seriously. But parents are allowed to put in forms describing their child (without coming right out and demanding a certain teacher), then presumably the principal makes a match. I also know the teachers meet and discuss which teacher should get what kid and basically put in their own requests. DD's kindergarten teacher liked me and liked DD, so not surprisingly, she ended up with DS the next year. I don't think it was a coincidence. The next year, I suspected that DS would do poorly with one of the first grade teachers (who is very strict and not very warm), and so I put in an input form stating that DS would do the best with a "warm and fuzzy" teacher trying to avoid that strict teacher. Boy was that a mistake, because the teacher he ended up with had absolutely no interest in teaching academics! All she wants to do is sit around and play the piano and have pow wows with the kids, I think. Any parent who wants appropriate work is "pushy". So DS did not end up getting the teacher that DD had (who was fine), he got the warmest and fuzziest, who was also the most passive aggressive and hostile, ironically, and it was a disaster. If you know who you want your DS to have, you should make it clear to the principal. If you don't, all you you can do is say what kind of a teacher you are looking for and hopefully they'll do the right thing.
This other parent with the IEP--she always got the teacher she requested for her DS. I had no idea the teacher that DS ended up getting was so bad (at least a very poor fit for us), so I'm not sure how I could have avoided the situation. Even the principal didn't seem to be aware of how she refuses to differentiate. I did put on the input form that DS needed a teacher who can differentiate. It was just really bad luck.