I also don't know how a 4 year in the class would make someone 'uncomfortable'.
Marnie, you know I feel for you and your DS but I don't think I would let DD3 join a math group for 2nd to 4th graders because DD has made older children and their parents very uncomfortable in the past and one of these incidents involved math. We were sitting on a bench right next to a second grader boy who didn't understand his math homework. His mom was getting visibly upset and was starting to yell at him for not being able to do his homework. Sensing that the boy was in trouble, DD3 (I think she was almost 3 at the time) gave him an answer and tried to explain the concept to him. I whispered to DD that his mother was helping him so everything is okay and she could go back to doing her own activity. Needless to say, his mom got even more upset with her son and her voice got even louder. Tears started rolling down on his cheeks and we left. I probably should have said something but I couldn't think of anything appropriate on the spot.
In a structured group setting with a teacher to control the flow, it probably won't be as horrible but I am getting the look from other parents during library story time as DD tends to answers all the vocabulary questions with razor-sharp precision. This sometimes happens after older children give random answers so I can understand if other parents feel DD's presence is not good for their child's confidence. It's a sticky situation. I don't think DD is trying to outshine anyone but I suspect the positive feedback is starting to get to her head.
We're considering summer music camp for DD and it's a lot easier for music because some children have started when they're 3 like DD and it's perfectly understandable for them to be ahead of older children who recently started on that instrument. When it comes to academics though, both children and parents can be quite sensitive.
This is one of the reasons why I'm starting to feel GT education is preferable to acceleration.
