“If you want your children to fight for their faith, send them to public school. If you want them to lose their faith, send them to Catholic school.” Attributed to Ven. Fulton Sheen, but almost certainly not said by him.
It’s a variant of something that might have been said by him: “I recommend that my relatives send their college-bound children to secular colleges where they will have to fight for their faith, rather than to Catholic colleges where it will be stolen from them.” This form of the saying is attributed to him by Msgr. George Kelly in a 1987 Crisis article. (Thanks to David Smith for finding this.)
As always, if you want to prove me wrong, provide a documented primary source, please.