How do you rebuild & teach trust to your child?

I was told through one of the teachers today that my son (age 9) had given money to another student in his class amounting to $15.Our school has a fairly strict no candy / no toys / no money policy and we encourage all our children to follow that rule, it's not always observed by others and as a result our son comes home every couple of weeks with new trinkets / pokemon cards. I bring this up as previously another child gave our son a toy "for free" and the next day demanded a dollar for it to which our son attempted to oblige but was caught.He really struggles with this policy this year. About every 5 to 6 weeks we catch him trying to smuggle something to school (money, lego's, cars etc)…. Personally, I feel it's damaging our trust with him, I feel like I cannot trust my 9 year old son.His money was in piggy banks, I've just now cleaned them out to hold in trust…. I've noticed that his younger brother's piggy bank is completely empty, except a single penny and it wasn't like that before.He doesn't have any behavioural or learning issues, he's quite bright, near the top of his class academically, not a great athlete but he plays different sports and tries out for school teams all the same, he's got a wide group of friends that he plays with across a bunch of different grades.My biggest concern is the breaking of trust. I recognize there are reasons for him doing this and he isn't doing this to spite us, (we'll have to get to the bottom of his motive for giving $15 dollars away).He's done this before, this feels worse because of the quantity of money, but to him I recognize it probably doesn't really register. In the past we've talked about the problem, then taken television & video games away and then had him spend time alone in his room thinking about his actions…. and shamefully I've yelled at him about this.To be perfectly honest : Right now I am really steamed about this. I feel I cannot trust him and that he is deceitful / deceptive and a liar.I don't know what else to do with this child, how do I get the trust issue through that hard melon of his?How do you guys communicate the value of trust with your children? via /r/Parenting http://ift.tt/2roA5HC