For students who have finished a primer method book and are reading notes in a Level 1 book, I recommend the Preparatory Level. The Piano Repertoire books are graded on a higher level than lesson books.
For students that have been reading music for about a year, know most of their major scales, and are finishing the Level 1 lesson book, I recommend Level One in the Repertoire Series:
For students who have been playing the piano for about two years and/or desire more challenge, I would recommend Level 2 in the Repertoire Series. The pieces in the Baroque and Classical include many of the Bach Minuets that are often played in piano recitals, many from Anna Magdalena's Little Notebook. Students should be proficient in most scales and be comfortable moving out of 5-finger positions.
Students also benefit from theory books, particularly after the first year of study. I will recommend some theory books in a later post.
Back to practicing! :)