Dear teachers,
Please STOP IT with the "all girls sing this part, all boys sing that part of the song".
You have trans and nonbinary kids in your classes. Yes, you really do. Not all of them want to be out to you or their classmates. Not all of them feel comfortable with just picking a category at random; not all of them feel comfortable with just being quiet.
And they shouldn't have to.
Just find better categories. PLEASE.