[Timpanagos1]

“And besides, any student who did not feel comfortable singing it, was not required to do so.”

I bet they were also not required to sing Christmas songs.

[Campion]

“And besides, any student who did not feel comfortable singing it, was not required to do so.”

I believe the courts have already ruled that this argument doesn't fly WRT Christian prayers or religious observances. If it's sanctioned by the school (as opposed to being student-organized and led), it's an impermissible endorsement of religion, whether participation is mandatory or not.