If they still provide the same classes, just with new teachers, then no, you cannot rescind or terminate the agreement or get your money back: business, including schools, do not guaranty you will get the same employees or teachers as were in place when you first  signed up, and the fact that they will have new teachers is not a breach of their obligations so long as you will still get the same service(s). (Note: if they did in fact guaranty that your child would get a certain teacher and now he or she will not, that would be a different story; in that case, they would be in breach of their contract.)