My son has taken a GCSE modular assessment maths course. He has just turned 16 and would be in year 11 at a state school but is in a residential special needs school which doesn't split the years in the same way. He is the youngest in his class, all the other members would be in year 12. He had hoped to continue with this course up to the summer to enable him to achieve a top grade. His school has decided that his B grade is sufficient and that it will not continue with a maths course for his year group for the remainder of this year. Is this legal?