Remove the scales. Really, don't have them in the house. Sit him down again & explain that this is not about weight, that you were trying to talk to him about healthy lifestyle choices, he is fine just the way he is, he has lots of growing left to do. Then teach him healthy lifestyle choices by involving the whole family. Do active exercise together. Teach your kids to have an extra serve of veggies if they are still hungry, teach them to include veggies in their snacks. Get the boys in the house to do some make bonding things like taking on a cross country jog challenge or something, together. But most of all, get rid of the scales.