M.T.
I'm not big on rewards charts for kids past preschool age. I don't think I'd focus so much on the actual poundage, but on healthy eating and exercise. Don't keep things in the house that you do not want him to have, such as soda, kool aid, ice cream. Portion his food for him, and let him know if he wants seconds, salad or vegetables only.
I wouldn't have any expectations for weight loss at sleepaway camp. There won't be anyone to oversee his eating, he will have to choose not to eat the desserts or the punch and to pick the skim rather than the whole milk.
When school starts again, I would send his lunch from home if the choices at school are not healthy foods.
Good luck!