His mother is sabotaging him. Might as well as a kid to go without glasses.
Soon, it will be HIS decision and not hers. As an adult with ADHD, I can confidently say that if he ever tries drugs, there is a very good chance that he will never forgive her for screwing up the rest of his life.
That said, community colleges generally hand-hold a little more and are a better place for less than excellent students. The chances that he can handle all the changes with going away to college all at once are slim.