My oldest is 16 and was and still is,to a certain extent, the same as this. She lately seems to be getting more motivated as she is preparing for future life goals. It’s best to continue with the routine of summer school without missing otherwise they will start realizing they may be able to get away with this behavior in other situations. It’s only 2 hours a day, it gets them out of the house, and I bet he is glad he went by the end of the day. My now teen was always grudgingly glad I made her follow through even when it was a battle. Good luck