Hi! My daughter started in 3rd grade in the yellow book and has worked her way through green, she just finished up 7th grade.
She is a great independent learner who has no problems. My son, who struggles with english started in the 2nd grade in the red book. He is a great reader. It has taken him about 2 years in each book (red & yellow), I am debating right know if we will start orange or move into the purple in Aug. I have both, so I am out no money, just trying to see if he has had enough maturity growth and muscle strength to move up a year. So, my daughter is right on in the books with her grade, my son is behind in the grade by one year.
Hope that helps.
Vanessa