I read your post on the "requesting teachers" thread. I didn't want to hijack the thread, but I had to write back to share your pain! I teach in a private secondary school. Parents are not allowed to request teachers at my school, but some of it goes on anyway. It's not that the parents can just request whoever they want; it's that the people who make the schedule within the school will sometimes rig things instead of letting the kids fall into classes randomly. It happens when the parents are either VIPs in the school community or known PITAs.
But I hear you about the imbalance in class composition. I have a reputation with the administrators and guidance counselors at my school for running a very tight ship and being great with parent communication. Give you one guess which teacher gets the lion's share of difficult kids and parents! It's like the reward for doing a good job is that the school makes your job even HARDER!! It does get to be a stressful drain, when you know that certain people have requested you. The other thing that is unsettling is when you have a good rapport with an older sibling, and the parents beg the school to put the younger sibling with you... and then you can't seem to hit it off with the younger one. It's just awkward all around, because you know the parents are disappointed.
I had that happen with a family a few years ago. Their daughter just lives, eats, and breathes schoolwork. English is her favorite subject, and she did really well in my Honors level class. The next year I had her younger brother, who I think was put into the level on based on pressure from the parents and the assumption that the family smarts just hadn't manifested in the brother yet. (For the record, I disagree with this type of logic when making placements, but I don't teach the grade below, so it's not up to me.) Turns out the younger brother was fairly smart, but had a deep aversion to doing any kind of homework. All year, his parents kept insisting that something was wrong, and I kept saying, "Yes -- something IS wrong. Your son won't read the books or do any writing assignments. It's a problem for sure." I don't think that was the "problem" they were interested in hearing about, somehow....
High School English teacher and mom of 2 kids:
DD, born 9/06/00 -- 12th grade
DS, born 8/25/04 -- 7th grade