Would it be possible for him to take some interesting math, like discrete math or problem solving? I am thinking that if he already took a GT Pre-Algebra course this school year, there is no point in repeating it over the summer. I am also thinking that it may be equally painful to have to cover an Algebra I course twice, especially back-to-back. In my experience, high ability students don't need extra repetition as even once sometimes seem too much.