I'm an instructor for a university. The general principle that universities use is that anything you turn in, you assign copyright to the university. This means the instructor can use turnitin without violating copyright law. Is it right to require students to give up copyright over their own work? I don't agree with it, but it's not unreasonable. Most assignments are similar to "work for hire", written to a specification of someone else for a particular purpose (in this case, grading).
For public school, you can't choose whether to attend or compare policies between schools. In this case it is the government stealing intellectual property of its citizens. I applaud the kids for standing up to it.