My daughter, now 10, has attended her last two 504 meetings. She was able to give her opinion on what she feels works and what doesn’t work for her accommodations. She mostly just read quietly to herself, but felt valued in being involved. I think as long as it’s a review and not the first meeting, it’s good for children, who are willing and able to be involved. Every child is different, as we know, and as long as you prepare him for what happens at the meetings , let him know he’s free to excuse himself if he becomes uncomfortable, or to speak up if he agrees or disagrees with what is being discussed, he’ll welcome the the involvement. You may want to bring something else for him to do if he needs a fidget or to draw or read to calm him. I hope this is helpful and wish you all he best in coming to your decision.