And each time they rearrange themselves, there's the incumbent chatter and turmoil. If you factor in all the packing up and settling down, I'll bet each transition interrupts actual education by at least 10 minutes. Put another way, a good two hours of the six-plus hour school day is lost to transition time. School isn't quite that bad. But it's the same idea.
Block scheduling is far from perfect.
But truth be told, those kids are the ones who exploit the current system anyway. All in all, block scheduling is the kind of reform that is necessary and overdue.