Is it legal for me to use an artist's song in a video for school?

As long as you cite the artist, song name, and recording label; and don’t sell the video or reproduce it for people other than those in class, or publicly let others view it.
That is what my photography teacher told us.

I believe the rule of thumb is: as long as you don’t charge admission to the assembly (or wherever you would show it), and as long as you don’t receive any money for the video.

I used to edit video for the Air Force Base here in Columbus, and we had a standing letter from the JAG office clearing us from copywrite violation as long as the video was shown for motivational or education purposes.

Not legal, but who cares. You should probably pay around $500 for doing it.

Yes, you can use materials so long as they are for educational purposes. This is how your teacher is allowed to show you say, a movie in class, or a television show they recorded. Since I’m assuming it’s some kind of project, legally you SHOULD cite probably the artist, song name, and label yes. But I doubt if you’ll get in trouble if you don’t.