I think it is best if you can get some accommodation in the classroom; I'm sure he will need it. It's worth considering different approaches, though. Mixed age instruction can work well. My daughter is in a mixed age classroom now and it helps. It often takes creativity to work out good solutions, though, unless you are incredibly fortunate in finding an appropriate school. That's why I think it so important to find a school willing to work with you and with a positive attitude towards academic achievement (most schools say they value academic achievement, but it's less common to find schools that really value kids who don't fit easily into a regular classroom and need additional help). We have often felt like fitting in and doing well on the standardized exams was valued more than exceptional achievement.