My older one insisted on reading all 46 Magic Treehouse books, in order, when he was in first grade. so we bought them online and he read them all. He's read those Rick Riordan books, Percy Jackson, in third grade, and now he's reading other things that he's written, now that he is in 4th grade (they are listed as being 6th-8th grade level).
Perhaps fortunately, my now second grader has refused to read the Magic Treehouse! So he's reading some Bailey School Kids, which are at a 4.5 grade level.
I agree that esp. younger kids like the repetition. My older one really got alot of confidence out of reading all of those books.
