No, the level numbers are not the same as grade levels, although after completing all 10 levels a student would be at a 9th grade reading level. At this level there are no more rules to teach, and the student can read anything – even college textbooks.
When tutoring young children, we stop at level 8. With this, we see children go from being a poor reader and speller one year, to being at the top of their class the next year. This is does AMAZING things for a child's confidence and self esteem!
Levels 9 and 10 can be taught to children in the 7th grade and up. At this point they should have enough vocabulary to handle those levels. If not, work on growing their oral vocabulary and delay those last two levels until seventh grade.
Levels 9 and 10 (Influence of Foreign Languages, and Latin Roots and Greek Words) ideally would be taught starting in seventh grade, before a child enters high school.
Those two levels will make certain that the student can read and spell all of the mature words they’ will encounter in high school and college science, history, and math courses.