No punishing, that's only going to make S feel worse. When a child is demotivated punishing them isn't setting boundaries, it is forcing them worse.
Your S isn't misbehaving or doing this deliberately, it's because of his life sitch and he's demotivated. HE isn't diving off and drinking etc with his buds.
How about organising extra support for him instead and offering to guide or get guidance by a teacher on it. You will do better by getting his buy in.
So S what can we do about this? How do we get the projects done.? Would a rime extension help? What can I do to help and support you? How can we get your game consul back quicker? Etc....
So what do I mean when I say a loving R with both parents may not be possible?
As a question of fact it isn't. Some parents and some kids aren't loveable. It's a limiting belief of yours that it should be, absolute thinking as a flaw. S has the right to choose not to love his mom. He has that right although I suspect it's devastating for him, especially if it is insisted he does. Love is a choice and S can choose to not love at this time. Or he can love and still not want an R with his mom.
V
Freedom is just another word for nothing left to loose. V 64, WAW