Great questions above. What's the school's level of understanding of gifted learners? If it does not include understanding that sometimes, the lack of challenge or slow pace can increase behavioral issues, perhaps you can share some of that information with them. Advocating for a trial period based on his scores would be worth a try, too. Do they know about his diagnoses?

However, if this is going to be a class for perfect little angel students, it might not fit anyway.