I have learned most of what I know about homeschooling by making big mistakes in our house. So this bit of wisdom is one of those things that I learned after wasting several years and lots of money doing stuff that didn't work.
If you want your son to say... learn math, play the piano, play chess well, learn animal husbandry, be fit, write coherently.... be a grown up, then do everything you can to make it a non-fictitious activity. It's not always obvious as to how to do this, and then, when it becomes obvious, the stakes can be a bit high.
We (so actually...Jason) are Tech people. So we got these crazy EV3 Lego bots. You can program them and make them do cool stuff like follow lines and go through obstacle courses. We got them for the boys about 6 years ago and they sat on a shelf for a good 12 months. Then Jason signed them up for the IEEE Robotics competition: a few hundred school kids, extreme social pressure, the potential of winning $500 in Lego prizes. That somewhat rash decision started what has become a big part of our homeschool routine. I think it was the seed that got Gabe into programming. They got into the EV3 because it was going to be really embarrassing showing up at this event and getting totally pummelled. It became real to them and the stakes were pretty high. In one of the STEM competitions, we are consistently the only homeschool team and it is very obvious - we are the only team with less than 6 students and we are always the only team with a grade differential of seven years between teammates. We're on display in front of the public school board. We all feel that pressure.
Chess - I have always scheduled in chess a few times a week in my September timetable. Want to know how often the kids have played chess this year? About zero times. Zero. It gets shuffled out. We forget to make time. But if you call their friends' moms and set up a chess tournament with a few kids who you know take private chess lessons... well they've played chess a lot this week. Again, the stakes are higher. I am pretty sure we are going to get creamed, and there will be 10 youthful boys in my kitchen for an afternoon...
So all this is to say, I think kids really see through pointless activity and teen boys see through it the best. Even when the goal of the activity is truly noble and needed, boys have a hard time getting behind a pretend assignment. Your kid needs to learn proper letter writing, write to your MP about how stupid legalizing pot was and how you now have a grow op in your backyard. Get them to take notes in the sermon and have the pastor review them later in the week (or threaten to). You think your son needs to be... um... toughened up a bit? Hire him out to someone who needs some heavy lifting done and who has a noticeable lack of empathy. Or get a horse. Or drop him off at Eglington Station with a pink shirt on. It's not always possible, but it often can be made possible with the promise of an afternoon of chess and snacks.