My 12 yr. old usually steals from family. He doesn't steal from the school or stores so that a relief. He usually takes from family.

Perhaps steal his stuff and let him/her see how it feels.
If your 12 year old doesn't get an allowance, have them do work/chores for money.

Does he understand what he's doing?

Does he understand the concept of consequences? Right and wrong?

Are there or have there been any major issues going on in his life?

How's his school work,his behaviour in school?

How is his behaviour in general?

Is he secretive? Or open?

More questions then answers right now,if you could give a little more information it would help towards giving a more comprehensive answer.