ATOS Readability Formula for Books

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.

Administrators can choose the preferred book level to use in the software: ATOS book levels or Lexile® Measures. For more information, see More Information on Lexile Measure Preferences in Accelerated Reader and Star Reading.