Here's what I do....
Identify a particular section that needs mastering. Most recently my daughter was forgetting to play E-G-F# before playing F#-E-D on the last line of Allegretto in Suzuki Book 1. She was skipping the E-G-F# and going right into F#-E-D, which is actually the ending of the second and fourth lines.
Together, we identified this as a "quarter spot".
Then we began working on it. She could practice it as many times as she wanted, with me helping her. When she felt she was ready, she could present it to me, without help and if she played it correctly, she would earn a quarter.
We practiced. She presented. She failed. Try again tomorrow.
The next day, she practiced quite a bit more. I could see that she was really taking ownership of figuring it out, and when she was ready, she presented again. This time she was successful and earned the quarter.
But this is not the end of the challenge. In order to keep the quarter forever, she would have to present this section to me one more time in the next practice session.
The next day, I let her practice, with or without my help as much as she wanted before presenting it to me. I was so pleased that she practiced the section at least 5 times successfully before feeling confident enough to present it to me.
She was successful, and now she's 25 cents richer. She also knows the ending of line 1 quite well. A big return for me on my investment!