Hi,
I don't have experience with dual immersion, but if you like everything else about the program and math is the only issue, I would recommend the part-time HS and/or afterschooling in math. If possible, could your DS be excused from the math at school altogether if he's already competent in it? Would they allow him to do online math at his own pace (Aleks or EPGY, eg.) while the other kids are doing math? Is there any possibility of a bilingual tutor going in to teach him math, if the school is not keen on online programs not in that second language? (Although I'm guessing there are probably online math programs in different languages too...)
