I think you need to talk to him It's not about grounding or ungrounding him - find out why he didn't care and why he tried hard during the summer. Something motivated him - find out what it is Since he was grounded during the school year and did terrible - I would argue that grounding him wasn't an effective punishment. You may need to consider other consequences that might mean more to him. Lastly your son needs to know you care for him and why grades are important to you. It may b difficult to convey the ideas of career and college but u can discuss the importance of work ethic and excellence and character.
I think its your fault he's a dumbass. You gotta work with em when they're young man. He's never going to be good atb math now
1) You should let him leave the house and not sit inside all day with nothing to do... 2) Why ground from books? 3) Yes, unground him, show him that good grades bring rewards.
I think OP has more mental issues than I do, and... I'm an egocentrical masochist with a sadist's point of bleak! (Any cool people get my reference?)