The teenage boy was not doing well at all in public school, so the parents decided that it would be time to send the lad to Catholic school for the year.
At the end of the term, sure enough the son's marks were straight As.
The parents were overjoyed and asked their son, "How did you improve so greatly? Are the nuns that much better teachers?"
"Not really better teachers," said the boy, "but everywhere I looked I saw a man nailed to the cross, and I knew they meant business here."
BAD JOKE DISCLAIMER: We recognize that religious humor can be risky. It is our hope that by laughing at ourselves (and others) we can make this subject more approachable. If you find any of these objectionable, we apologize. As with most jokes, the original authors are unknown - but we thank them.