What helped us (and should help you) was having a strict routine. School work during school hours. Most important. Outside that, I do allow all sorts of other things - he can do his schoolwork in his pyjamas if he wants. He can do it on the floor, on his bed, or on the dining table. I have found that different subjects are done in different places.
Sometimes he's not able to cope with his usual subjects (he mighty be having a bad day for all sorts of reasons) so I have my own mental priority of what subjects to get him to do, when he needs to be grounded. The last resort is to let him watch a documentary or play a computer game that is also educational.
Before we made the switch to Distance Education (the kind of correspondence we are using - state-based, so it's cheap but very good) difficult child 3 had been struggling in mainstream, and also mysteriously ill. It turned out to be severe anxiety, but he spent most of one year at home with me. I was not going to reward him being sick with a holiday, so regardless of whether he felt sick or not, he had to do schoolwork during school hours. The only way out of it was for him to be in bed asleep. He rarely sleeps unless he really is very sick, so this way there was not a payoff for him to say he was sick and stay home.
While I was trying to educate him myself informally, we discovered his knowledge was woeful. At 11 years old he had no idea of where Australia was on the globe. No idea where Europe was, where the US was or anything. No concept. A lot of other stuff he's allegedly been taught, was just not in his head. So I let him loose on "Where in the World is Carmen Sandiego?" and although it mostly plays like a game, it helped begin the mental connections to various places in the world. I was horrified that we had to do this, but glad I did. So even though it was school hours, I was letting him play a game. He liked that - I made it clear that it still qualified as schoolwork, and there are a lot of other fun things that qualify as schoolwork. As a result, I let him suggest things he wants to do.
Something else we do - on Aussie TV on the ABC, we have on weekdays during school terms, some good educational stuff. It's between 10 am and 11 am weekdays (Aussie time). I know some of our TV programs do make it across the ditch - does the ABC stuff make it to you? I do know a lot of it can be also obtained via podcast or similar.
These TV programs span from K-12. difficult child 3 watches all of them, including the baby stuff. We have noted that a lot of his early learning was missed, so we let him watch the baby stuff even the early reading stuff. He seems to learn holistically, so it has helped him consolidate his learning. Some of the shows, though, have been senior high school Chemistry and senior high school Poetry. He's watched them over and over, even though I didn't think he was able to understand it. Then when his schoolwork caught up with the poetry (last year) it paid off big time.
Our routine - difficult child 3 gets up at about 8.30 am, takes his medications. I try to get him started at 9 am - tricky. The first hour is transition time. Whatever he gets done is a bonus. At 10 am he stops and has breakfast while he watches the TV educational stuff. Then from 11 am, it's back to work on whatever subject we've chosen for the day. He does best when we don't change topics, but let him complete a unit in one piece.
When we need a break - sometimes we go for a drive to somewhere nearby to do some practical stuff. For example, one day difficult child 3 was watching the educational TV and said, "I'd like to have a look at mangroves too." So we went for a drive (five minutes away) and walked through the mangroves. When we've been on holidays difficult child 3 writes a journal, trying to cover as many school topics as possible. He also takes photos and puts it all together. When we were in NZ he wrote about 20 pages (including the photos) and covered geothermal energy, vulcanism, continental drift, bungee jumping (we were at AJ Hackett!), gold mining, the weather (freak snow storm), Lord of the Rings (we took photos near where they filmed Hobbiton but baulked at going there), Waitomo, Rotarua and Lake Taupo. It was a month-long school excursion for him. In the evenings and mornings he did his Maths work (not Mathletics, but bookwork).
The routine is what works for us. It took a while but over months to years, difficult child 3 has become much better at organising his own learning. I can now go out for the day and leave him at home, knowing he will get some work done even if he is alone. It is better when I am home, though.
I do spend a lot of time and energy on this, but given his problems, I consider what I am doing to be an investment in his future.
I use his favourite subjects to help calm him, and to a certain extent to encourage him to get the more challenging work done. "When you have finished that page of English, you can start your next Electronics project." I've even used MAths to calm him, especially if he's getting anxious while we're on holidays. He was really terrified at Rotarua, had a strong sense of dread and was feeling like he was dying. It was a difficult day for us, but looking back I am glad we went through it and he is glad to have been there and seen it all.
These kids can be very intense, in the effort we have to put in. I'm further down the track and beginning to see the payoff.
I also had difficult child 1 studying and finishing his schooling via Distance Education, so I have seen this work before.
Marg