Paulears and PG have it right and I agree with other posters here
I do appreciate it's a worry and I have a friend facing the same dilemmas and it will be us next year
I think it's a done deal DS won't be doing drama and dance at GSCE, I hope we can fit music in though
He needs to concentrate on the academic side and will be choosing those options. He is lucky to be grammar streamed and although it doesn't come really easy he finds it easier than some of his classmates do, but needs to work hard, and be kept on task and nagged to do homework!!
The standard of dance at his school is poor IMO for all the reasons Paulears writes about and I'm not prepared to waste the school timetable on it. He gets plenty of great tuition out of school for all the performing arts and dance he does. I want him to stretched and pushed at school and I know this wont happen, the classes will be geared to the majority and I've seen the school productions ...

. Music however is good there, the head of department very experienced and motivated, lots of instrument tuition and learning to sight read.
Of COURSE if I could afford it I would have him at Tring or Contis full time, but that ain't gonna happen so we have to search out the best we can give him out of school hours.
I really think your DD will make it if she is meant to with or without drama and dance at school, it's all about the audition and the level attained with relevant exams like Trinity, Rad etc and on the job experience, confidence at auditions etc.
And not putting all your eggs in one basket as far as school is concerned ?
