Teaching My Son to Be a Man of His Word

Been thinking a lot about this lately. My old man made me shake hands and mean it. You give your word, you keep it, period. Now I'm trying to instill that in my 12 year old and it's harder than I thought. He wanted to back out of helping his scout leader because his friends were doing something else. Told him a commitment is a commitment and we don't renege on people who depend on us. He did it, and afterwards he actually felt proud. That's the kind of man I want him to become. Anyone else dealing with this with their kids?