What are Schools legally allowed to block via internet filter? (TRECA)?

This is it. They finally out-did themselves. *applause* There is a "Music Appreciation" filter on Treca. I honestly see no reason such thing should exist. I was simply looking up the lyrics to the Rise Against song "Rumors of my demise have been greatly exaggerated" and I come to a BLOCK. I instantly become curious why they would block such a thing. My first line of thinking was maybe it had some inappropriate content. Nope! They blocked it under the category "Music Appreciation". I don't know anymore!