I need advice: Trust & Peer Pressure among the playground set.

Our elementary school has a no toy / trading card policy for the children. My wife and I do our best to honour that policy and encourage our children to do the same.There is a child in our sons class (Zach) who is very persistent about small collectible toys (think shopkins, lego minifigs, pokemon cards etc) and who has no problem bringing his toys to school. It's been a problem since their days in Kindergarten, Zach's mother makes no bones that her children are exempt from the no toy rule.From past incidences with some of Zach's siblings we have a pretty good idea that Zach's mother is a "not my child" sort of parent, thinking their child would never be capable of X, Y or Z.Zach and our son have been in different classrooms for Grades 1 and 2 and recently found themselves in the same classroom in Grade 3. My son seems to really like Zach.At the start of the school year (early Sept), our son revealed that Zach attempts to coerce him into bringing his small toys to school to trade. We've told our son the reasons why the school doesn't like toys at school and why we are supposed to follow the rules, he seems to understand this.Two weeks ago our Zach gave a toy to our son at school. The next day Zach decided he needed something in return. Unbeknownst to us, our son took some money from his piggy bank to give to Zach.We explained this situation to him (giving requires nothing in return) and talked about his friendship with Zach, and what our Son wants in a good friend.This morning we caught our son with 5 small toys (that were his sisters) in his backpack... Again for trades at school.It's not the toys, it's the trust. This breaking of trust breaks my heart.I recognize the core of the problem right now is something that I may not be able to control. We all understand the effects of peer pressure and how hard it is for children to make good decisions. We understand that a big chunk of this issue is indeed Zach, We cannot control that, but we want to encourage our son to make good decisions (aka follow the rules).Does anyone have any advice to offer how to further encourage our son to make good decisions with his friends and not break trust at home? via /r/Parenting http://ift.tt/2cwrKGM