I was about the same age - maybe a year older - when I stole a clip-on bear from a shop. They were a bit of a fad back then. The shop had a massive tank of them at £1 each and I couldn't have one. I already had one, but I wanted another to keep it company.
I looked at the massive tank of all these hundreds of clip-on bears, knew that really, no one would miss one, that it wouldn't put the shop out of business etc, saw that no one was watching, and pocketed one.
Later my mother realised I had two bears, not one, and gave me this long spiel about how "sad" the people in the shop would be when they realised one of their bears was missing.. I remember sitting there and losing respect for her by the second.
The shop weren't going to notice they were a bear down and if they ever did, they were grown adults, they weren't going to sit there going boo hoo hoo over a 2" toy bear. Come on. I knew she was talking nonsense, I knew she was trying to get a message across to me, and I couldn't believe she was doing it in such a stupid way.
What would have been more effective? Straightforward facts. And I mean facts, not threats. If you steal things, no one will trust you. You won't be invited to people's houses. No one will let you wander into a room on your own, there'll always be someone watching you.
Yes, there are things you want. It's normal to see things you can't have and wish you could have them. There's nothing wrong with that and everyone understands that. But it's not okay just to take. It's okay to borrow, it's okay to take something home if you've asked to borrow it. But if everyone stole all the time as they pleased, we'd never be able to find anything.
I don't know. I'm not an expert. I'm just saying what would have worked better for me than my mother pulling theatrical sad faces and talking rubbish.
I wonder about the teacher making a big fuss about the return. I wonder if it might encourage him to do it again. Maybe she could make a bigger fuss if he asks first to take something home and then brings it back, just to show that that behaviour's preferable.