Wow okay, you might find this as “unacceptable laziness”, but speaking as someone who’s been in a similar situation before, constantly telling him you believe he can do better and that you know he’s not trying his best will only discourage him. He may not be doing his best in actuality, but if his judgement really is clouded by something else, he likely believes that he’s doing the best he can. Not to mention that children and teens nowadays are given much more schoolwork, higher expectations, and are generally 10X more stressed in general. Just let him know you’re proud of what he’s doing now, even if you’re not. It might seem like it’ll justify his performance in his mind, but if he sees you’re pleased by performance he himself isn’t proud of, he’ll likely try to gain that praise again in the future by working harder.