Appleville Elementary series by Nancy Krulik

You want a series that is beyond the beginner reader books but not so long the kid gets bored reading them? You want an author that has plenty of series to choose from? Then Nancy Krulik is the author for you. The Appleville Elementary is a great introduction for chapter books. Then she has written Katie Kachzoo series, a girl band series, and "How I survived Middle School" series.