Hi there,
I was in a similar position to this when sitting my GCSE's many moons ago now, and was to be withdrawn from 2 exams but you can actually pay for your child to sit the exam and then if(no scrap that, when!) they pass the school can refund you. Please don't let your school bully you, sit down with your child and see if they think they would be able to catch up the course work, if not allow them to be withdrawn and then they can concentrate on their other subjects!
I hope this helps, good luck to you and your child(especially at exam time.
Blessed Be