I go to a state school myself, however have friends who go to private schools. In my area anyway, kids who want to achieve but may not be intelligent are put into lower sets with kids who do not want to work at all, and therefore have a negative impact and those around. My friends say that at their private school, the guys who are in lower sets at least want to achieve, whether to impress their parents/friends or they have to work to stay in the school. I think thats the difference between them personally.