I don't see why not, and it certainly wouldn't hurt to ask the 504 team if this could be added as an accommodation. However, I don't know if the school will agree.
When you say he was "tested," was he tested for academic achievement or just behavior? You might reach out and ask for additional testing - something else might be going on such as dyscalculia. Also, depending on how low his scores are in math, he might qualify for an IEP, which would give him specialized instruction in math - hopefully in a manner that works for him.