Thank you all so much for your input so far. I find myself feeling a bit upset reading the thread as it's such a difficult decision.
Answering some questions:
I haven't discussed it with my child as it is a very difficult discussion; I think they know that the academics is sub par, and that they are missing out, and that they are bored some of the time. This decision is massive, can a thirteen year old have enough input, I know I didn't have a clue at that age!
I think this vocational school is meant to have better academics than others, so not sure transferring would make things better
We are about an hour from London so could easily get in to the associates there. Our local school was okay, and I think could accommodate them, I think i will speak to the ballet teacher again about what might be possible.
Yes, we would be in a better position to give more to the dance if they weren't at the school.
Yes, I believe the school has been affected by same academic shortages in teaching.
I think I agree about the academics being able to be done later, but think that GCSEs should be done now, plus as I mentioned dc is really quite bright.
Please keep posting, this is really helpful!