> Why are the students sitting in groups and cutting paper with scissors?

Because paper cutters are too easy to disassemble as re-use as a shiv machete? And anyway, it's pretty hard to make cloudy curves with a paper cutter.

> in the American class the teacher spends practically 0 time at the blackboard, the students sit in large groups, the teacher spends most of the time with one or two groups.

Three or four students is a large group?