Lyn, that is hilarious! (Both -- about your teacher, and the story of how classes are put together).
In my experience as a former teacher and special ed instructor, Lyn's more or less right! Except I wouldn't use the word "bad." Especially since my own daughter is one of those kids.
The way it worked: We looked for the kids who had exceptional needs. My job, specifically, was to try to get a real sense of their learning profiles and then create the best "match" for those kids with the teacher -- as well as to divide them fairly among the different classes. This was a delicate balancing act in the high school grades (where I worked).
We tried to make sure each class had a fair mix of boys and girls. We tried to ensure that inexperienced teachers did not get burdened unfairly with disciplinary problems. And so on.
For a kindergarten class -- did the children do a reading readiness test before entry? Were they interviewed or did you fill out questionnaires about them? If so, there may have been a similar sorting process. They may also be age-sorted (born early in the year/ born late in the year) because children's age on entry has been shown to affect attention and distractibility levels.
In answer to your second question, yes, it is (or can be) annoying (and sometimes quite difficult) for schools to make a change after the fact -- but a lot depends on the reasons the change is being requested and the way it is requested, of course!
And, the fact that it might be annoying is no reason not to do it if you have strong reason to believe that leaving things as they are might not be in your child's best interests. Schools don't know everything about your kid. As parent, you are your child's advocate. If you actively believe that your child could be adversely affected by a placement, it is perfectly okay to speak up. Just know that you may be branded as a "troublemaker" -- and choose your moments wisely and well.
I say this as someone who has had to be an extremely active (even vociferous) advocate for my daughter's needs. I have sat on both sides of the desk and I know what it is like -- but if I think my daughter is being shortchanged, I will not settle for that. Her education is too important, and I don't care what people think of me. At the same time, I aim for diplomacy and tact first. The iron fist only when absolutely necessary.
To my mind, simply not knowing the teacher doesn't sound like all that great a reason to request a change. You could ask for information about her or him first -- and maybe then make a decision. After all, the good you don't know might be better than the good you do know!