He is old enough to be part of the decisions about his education. WHat we would do, is a "PMI". That stands for, "Plus, Minus, Interesting". You sit down together and make a list of the good points about going back (vs continuing to home-school); the bad points about them; and the other points that are neither good nor bad, just worth mentioning. You need to both sit down and put all cards on the table. He also needs to feel free to say what he feels, without you getting upset. For example, if he says, "Your lessons are boring," you need to not get offended by this and say to him, "Can you think of a way I could make the lessons more interesting?"
Similarly, he needs to not get offended if you say, "I find it frustrating how I can't get you started easily on s topic; sometimes you just seem too distracted and don't work well."
The aim of this is to resolve the overall problems. It also should help determine what he hopes to find back in mainstream.
Then if after all this you both agree to give mainstream a try, he has a benchmark by which to assess the success or otherwise of this change in direction. After a couple of months you both sit down again and discuss - "How is the reality of mainstream matching with expectations? Are you getting what you hoped? Are there any issues you hadn't been able to plan for? Is the choice still a valid one, or was it a mistake?
After a process like a PMI, you find it is easier to change direction if expectations don't match what you predicted, because it's like having the rules changed on you. For example, if he says, "Bullying won't be a problem any more because I am more skilled at handling it; plus this school doesn't allow bullying, they're really good with it and anyway, kids my age are more mature than that," but the reality shows that bullying is still going on and he has become a target for it once more - well, the forecast was a good one based on information available, but you can't predict how much people (the ones who told you it would all be OK) are capable of self-deception.
The thing is, whatever decision is made, he needs to have ownership based on full and frank disclosure. It makes it easier to make considered decisions later in life, also - he needs practice in making his own choices, and beginning now is good.
In the process of the discussion, you might find that what is bothering him could be more easily solved by a small change in how you do things. For example, a concern often expressed by people about difficult child 3 being pulled out of mainstream, was "What about his social interaction? Because of his autism, he needs more, not less." It was a serious concern, but when we looked into it and especially when we actually began the home education, we found it was not the problem we expected.
So - find out WHY he wants to go back, what he hopes to achieve form this and then discuss if there are other routes he could aim for. For us, if difficult child 3 said to me now, "I want to stop studying correspondence and go back into a face to face classroom," I would NOT go the high school route, but I would instead enrol him in our adult education college. It actually goes beyond high school but can take students still at high school, but in a more career-directed way. So he could study ONLY computer-based courses, if he chose. Or only graphic arts. If he did well after a couple of years, he could then go to university, where a good portion of his college studies would be given credit, helping him bypass first year uni certainly, and probably a good part of second year or more.
The aim is education, on a broad base. School is not necessarily the only option.
Marg