I have a couple of thoughts:
1) Reading both the article and Knight's comment, it does sound like they were blocking traffic and it was not well-planned. However, if it wasn't malicious they should have been applauded for being pro-active, and then talked to constructively about how to better plan next time. They are teens after all, not professional event organizers. They can't be expected to plan a large event perfectly, and it is commendable that they tried at all. What a great learning experience that could have been (and, in a way, was).
2) It rubs me the wrong way how much control school administration has over kids, on campus and off. Yes, these kids were waving school flags, but I've read a lot of articles in the last few years about dictator-like behavior of admins and it doesn't seem right. Anyone remember the girl who was strip-searched when another student accused her of having Ibuprofen (she didn't have any)? Unbelievable is an understatement. The principal reversed her decision for the bikers, but it shouldn't have been made so quickly in the first place.