Every once in awhile I think it is important to remind them of their commitment and of consequences, especially when you catch them doing the wrong thing. I think that sending them home was maybe even a greater message than yelling. If you're not going to be here working hard, then go home. Don't waste my time (that's what I'd be thinking).
That was a tough session, but also fun!
Yeah, agree with Sam, I bet being sent home made them go "woah..."