if they don't mix up the grouping like that....
what will happen if let's say the group with all the express students win the 'Best Group' or something, then you all will cry for foul play too. by mixing u all up like this the 'Best Group' thing becomes a fair game.
random grouping happens everywhere la. i've organised about 2-3 inter-school camps and been an instructor in several camps, be it school based, or national based, but yet I dun see such 'stream discrimination' problems happening anywhere.
during the camp, everybody is equal. everybody looks and behaves like shit inside camp, cos all wanna go home

, but eventually you'll find that some of your best friends ever are your camp mates from the same group.