I like polarbear's idea. It would allow him to keep doing what you are doing now with the good teacher, and then skip over the bad teachers. Would the school be willing to approve a skip for next year instead of for now? It would probably be easier on him to do the skip at the beginning of a school year anyway, rather than in the middle of this year.
However, if his current school is offering a skip and you are definitely wanting to do it as well (ie., it is just a matter of the timing), you should definitely do it before he switches schools just in case the new school wouldn't be willing to skip him on its own. This way, the skip will have happened and the new school would have no choice but to honor it because he will have already had at least a year in the higher grade.
Has the school offered a skip or are you just trying to figure out what would be ideal if they were to offer?
