It was only years later that I went back and tried to understand the intake process. I was blown away by what I realized.
The key to it is this. These kids absolutely HATE the experience of lacking executive control, in a classroom. Teachers have no idea how often they launch verbal attacks, but it is sheer misery for the kids.
Then they encounter this program. The program sits them down. Explains how it works. Lets them poke around. Talk to the kids in the program. Verify that it really works. And lets them know every rule, and every reward.
Then the program tells them, "You can't come unless you have completely internalized it. Every time you fail, you must remember how badly you wanted to succeed. We can't give you a second chance. If you have any doubt, prepare yourself longer."
Separately we parents are told, "This has to be your child's choice. You cannot try to convince them in any way. If you try, we will know and your child will fail. If your child asks questions, answer them honestly. If your child says that they are ready, ask them if they are SURE. If they say yes, then they can come. Not until."
And now the kids are caught. They absolutely know the tiger that they want to escape. It is their daily life. They absolutely know that there is an escape. They know how it works. They know that it works. And they know that it won't work if they have any doubt. Every last rule. Every time they hear it. They must WANT it. For 2 years.
It took my son about a month and half to declare himself ready. The first few months were misery for him. But I'd never seen anyone so determined to succeed. And succeed he did.