Tests out at 12th grade level? Are you talking about scores on a test like the WIAT? Or could he test out of most H.S. math classes?
Sounds like it's time to go into school and ask to see this teacher. I find when I'm not getting a response by email showing up helps. If you can't see the teacher, ask to see the principal or vice principal or head of the department. Even without the 504 your son should be getting an extra day to finish homework if he has missed school for an excused absence.
According to the Performance series tests, his scores are on par with a median 12th grader. Also, he and I took an online calculus course over the summer and he clearly understood the material at a fundamental level.
So far he is not being marked off for late assignments. My current issue is that his missed assignments are often due to the school not communicating those assignments to us.
