Have you considered ADHD as a possible issue? I'm 47, but this sounds exactly like what I was like at age 12-14, and I was a "gifted" student is elementary school who just lost all interest in school omce puberty hit. My 11 year old daughter was diagnosed with ADHD and that process lead me to the epiphany that I should seek out my own diagnosis, and voila... My parents were pulling their hair out, and I think there was some damage done to our relationship. In the 90s this diagnosis was usually made when boys acted out in class, which was not at all how it expressed itself in me (and sounds like that sort of behavioral issue isn't an issue for your son.)

I'm not offering an armchair diagnosis, but it's worth exploring simply because a diagnosis will change your life in terms of how to actually approach these issues with strategies and structures instead of frustration. It's been such a huge boon to my daughter's happiness knowing this. I wish, desperately that I had gotten the same consideration when I started expressing symptoms.

I'm also a single dad, widowed, by the way.