At this stage I prescribe the amount… but my son is only 7.
The URtheMom person (don’t have time to check her name) wrote an article that she offered for free on another board, and I did get it. You may want to email her and see if she will give it to you?
She starts out with her children prescribing what they do, and they check it off. But once they are to a certain agegrade, she transitions them to goal setting, and them choosing how much to do on any particular day… with the requirement that they must do SOMETHING in each subject every day.