Yeah, catholic was the PUBLIC system in my home town ( an oddity around this province), and it was the same: non Catholics, like the two Pakistani teachers, and also the OTHER CHRISTIAN denominations were not required to participate either.
It was funny, the "EVANGELICAL protestant" teacher with "JESUS LOVES YOU!!!" painted all over his MG in hippy scrawl got to do his own thing, and was never at the catholic functions we had to attend, which everyone had a good laugh about...
( The lucky SOB we were thinking. )
However in the PRIVATE separate high school there were no other denominations attending, being Catholic was a requirement to get in.