Are you sure about that? All kids in our parish school attend Mass every Wednesday, Catholic of not. It's the same at the H.S.
Make that 'Catholic OR not'...
Maybe during the school day they have Mass.
But in at least one high school they made the religious studies classes optional a couple years ago.
To your point, I have not done a first hand tabulation of who is going to church on Sunday and who isn’t. Just what I see and what I hear from parents.