Sixth graders are immature and still giggle when people fart.
Seventh graders are arrogant pricks who think they can do anything and it makes them cool.
Eighth graders are more mellow, but also arrogant. They've gained a maturity but there's always the handful who still talk about toilets and stuff filled diapers.
Once you hit highschool, those who haven't matured get weeded out by the community and shunned.