Dd is in Year 10 at a girls' selective indie. She's doing very well across the board but Maths has always been a weakness for her. She started Year 7 in the bottom set (out of 6) but with a small group size and excellent teaching she made very good progress and really started to get it.
She had great teachers in Years 7 and 8 and was moved up one set at the end of Year 8. Year 9 teacher was good too.
However she does not get on with the Year 10 teacher at all and I can see all that confidence she gained being lost. Her issues are that he is poor at keeping control, a group of girls chat and mess around and are generally disruptive and that this teacher has a couple of particular favourites who he calls on all the time. There doesn't seem to be a system of putting hands up for answering questions, dd says that you just shout out 
Dd says it's like he is only teaching 2 girls in the class and everyone else is ignored.
I know this is only her point of view but she is quite mature and honest and I trust her judgement.
I have brought it up with the school, teacher has been observed a couple of times but dd says it's better when he's observed and then it's exactly the same.
Dd really wants to move up a set but the school have said she's not ready as she's not at at the top of the current set. They all learn the same work, it's just the pace that's different. But there can't be a massive difference between set 4 and set 5 can there and dd feels that good teaching will over-ride any difference anyway.
Girls are always encouraged to see teachers at lunchtime or after class if they need to go over work again but dd is very shy and introverted and she just won't do this.
Do you think it's reasonable to bring it up with the school again or will dd just have to lump it?