I guess I would do exactly what you are doing. First pushing the school to meet your son's specific needs. Second going to the school board with the other parents to complain about the lack of "challenge" classes.

What I don't understand is what the "block" schedule has anything to do with it. Sounds like they are just using the change in schedule as the "excuse". My daughter was in a middle school that had a modified block, and my the H.S. runs a different modified blocks schedule. (Modified means.. that some days are block and others they attend all their classes.) Are they changing the number of students per class?