I can tell you that was my son when he first started HS. However we all knew the potential was there, however things just did not click. Until we took him to Kent States baseball Camp thanksgiving of his Freshman year. Then Kent State Coach, Scott Stricklin, sat all the young men down before the camp started and in no uncertain words, explained how important grades were. He talked about it for a half an hour or so.
After that it clicked for my son. His grades improved. He wanted to play in college and he knew there would be more options open to him if he was a good student. He also started taking a challenging schedule, instead of an easy one. He actually enjoyed school more and met some new friends, with a more academic bent.
I suggest if you have concerns, that you continue to try and motivate him and find what makes it click for him, so he does not become the kid in this thread.
I know this is easier said than done.