What was Jason's job/skill?

That's what upset me and confused me about his character... sometimes he would even give orders as if he was the mastermind by repeating what another member suggested seconds before him.

I think he's supposed to be popular, pretty, and powerful (headmaster's son)... at least before the movie starts. So "obviously" he's the leader.

So, not really.

He does sort of play a "creative" role, since he modifies the stamp.

In the end, he's really just the dumb muscle.