ATOS and Lexile measures are both valid and reliable measures of text complexity that provide a basis for matching students to reading materials. As with all readability formulas, the resulting value is an estimate of the understandability of the text. Accelerated Reader 360, Star Reading, and AR BookFinder display data in either ATOS or Lexile measures, based on the preference of your school or district.
Adapted from Appendix A of the CCSS for English Language Arts and Literacy.
For more on text complexity's reader and task considerations, read this blog post. »