that's terrible. my ds (also on the spectrum) also needed modifications with reading and writing in some subjects but our state allows an alternate coursework plan to be written into the iep that substitutes classes in the same subject matter (swaps one for another). ds didn't take some of the newer college prep level classes but b/c he successfully completed the swapped out classes (which are the same subjects just not cp/ap level) he got the same diploma as everyone else in his graduating class.
What state is this?
I am trying to do as much research into this as I can, because I really do want to argue this with the district. It seems really unfair. Unfortunately, our state has said that local districts can set their own (higher) graduation standards, so we might have no luck.