Hi OP, I have ADHD, autism, dyslexia, and mild dyspraxia. I tried learning to drive at 18 but despite having a nice instructor and doing all the prep work (and having a supportive parent encouraging me), it just didn’t work for me. I had another go when I was 25 and it did work, despite me being a lot more anxious and less confident by then! I did need more lessons than average, though - after three months of twice weekly lessons, I passed my test first time.
I would suggest that instead of paying up front for a large block of lessons now, just pay for a few lessons at this point, to see if your son is really ready. Then if he is, you can commit to the block purchase. (That would take additional pressure off him, he’d probably get stressed if he was a nervous learner knowing you’d already spent loads of money you wouldn’t get back if he couldn't make the learning from the lessons stick!)
I would also try to speak to instructors and find one who is known for being patient and encouraging. I don’t think you necessarily need to find one who understands neurodivergence per se - mine sure didn’t - but if you can find one who has those key qualities of patience and niceness and being reassuring, that’s ideal.
I learnt through BSM and this was back in the days where they had actual shops, so I went in and explained that I was super nervous about driving, very unsure of myself, had tried to learn years previously and it hadn’t worked, and so I needed someone who would be patient. The shop staff knew exactly who to book me in with. I know you won’t be able to do it the same way now - no BSM shops to go in to! - but if you can have that conversation in advance, whatever company you go with, it should save lots of stress down the line.