DS#1 is 9. What didn't work for him was radical acceleration or Montessori school.
We tried a grade skip and then another grade skip (so that he was 2 years above grade level) at the school's suggestion. The work was helpful, but he asked to go back to his grade level because he missed his friends. He also didn't have quite the executive function or organizational skills to manage the work. He could do all of it with direction, but couldn't manage a project quite the way an older kid could. He just wasn't mature enough yet.
Montessori also didn't work. He blew through the classroom materials too quickly and they had no idea how to differentiate for a kid with some extreme gifts. He was bored.
What is currently working is in-class differentiation. He is in a class with his age cohort and his teacher gives him differentiated materials to work on. He's working 3 grades above his current grade in several subjects. The expectations for time management and organization are age appropriate, though, which is much less frustrating for him.
