What state are you in?

ETA: I see it's Illinois. This law says that school districts have to make a plan whereby children will be "grouped and instructed in order to maximize the educational benefits the children derive from participation in the program, including curriculum modifications and options that accelerate and add depth and complexity to the curriculum content". There's also apparently an appeals process, etc.

http://law.onecle.com/illinois/105ilcs5/14A-30.html

Now, acceleration could mean subject acceleration-- but it seems like they have to do something reasonable. Perhaps subject acceleration would fit well for your son anyway at this stage, especially with your worries about maturity.

I know it's probably going to make you uncomfortable, but I'd start the discussions, yes.

Striving to increase my rate of flow, and fight forum gloopiness. sick