I think it is partly a girl thing and with whom they hang out. DD8 already seems teenager-like while her twin brother is far more child-like. I am not sure that the academic environment will make any difference. DD8 and DS8 are in a tracked class (around top 20%), which works one grade above although DS8 goes up an additional grade for math. In our case, it is partly the popular culture (tv., computer, older school mates).