You thought copyright law was criminal law. Copyright issues for the most part fall under civil, not criminal, law. Cable channels, PBS, certain artists, and others have authorized extended rights for schools. You thought copyright protection was created to protect people or enrich them. It was to benefit society at large.
Public education benefits the same society.
As new media take hold, it is often possible to apply older guidelines to newer scenarios. I would like to propose a rule of thumb I think will help. Before I provide this advice, I should warn you that I'm not an attorney. Ken Starr and F. Lee Bailey, just for reference points, are attorneys. Well, as you probably know, intellectual property attorneys are terrific to have around when you're in trouble or want the clear-cut rules of case law laid out as they apply to you.