ATOS Readability Formula for Books – Accelerated Reader

An ATOS level on a book indicates how difficult the text is to read. Thus, it can help you match books to a student's reading level. But the ATOS readability formula measures only the readability of the text. It does not (nor do any other readability formulas) take into account literary merit, sophistication of ideas, developmental appropriateness, or maturity of theme or language. This is why it's important to know and use three measurements when helping your students choose books: readability (the difficulty of a book's text), reading level (the student's tested reading level), and interest level (the content level of a book).

An ATOS level is often a good indication that a student can read a book, but may not mean that he or she should read the book. The interest level can help you decide whether the student should read the book.

Some pages in Accelerated Reader show both ATOS book levels and Lexile®* measures. If teachers want to see Lexile® measures instead of ATOS book levels in the Accelerated Reader Record Book and when setting goals and book level restrictions, they can use the class Lexile® Goals preference to choose "Use Lexile® measures" for their class. The preference also affects which levels students in the class will see (except where both levels are shown).