There are two possible starting points for Foundations: Level A and Level B.
For most students, and for all children just beginning to learn to read, the best starting point is A.
However, students who know all the sounds of the A-Z phonograms, can comfortably write the lowercase letters, have strong phonemic awareness skills, and can read unfamilar CVC words and short vowel words with consonant blends (ones they have not memorized as sight words) may in some cases be best served by starting in B. More guidance on starting Foundations at B.
When in doubt, we recommend doing at least a quick review of the material in A, as students will be more successful later on if they have strongly developed these foundational skills.