Study: ATOS an effective measure of text complexity

Renaissance Learning announced today that ATOS, the readability formula incorporated in the Accelerated Reader program, was found in an independent study to be a valid, reliable measure of text complexity as required by the Common Core State Standards (CCSS) for English Language Arts.

The study, "Measures of Text Difficulty: Testing their Predictive Value for Grade Level and Performance," was conducted by Student Achievement Partners, LLC. The research sought to measure the viability of existing text complexity metrics used in K12 schools, focusing specifically on whether the readability metrics support the goals of CCSS to increase student achievement.

CCSS, now adopted by nearly every state, represent a set of core expectations for student knowledge and skills that enable high school graduates to succeed in college and careers. The standards emphasize the need for students at all grade levels to read and engage in texts of appropriate complexity.

The research compared how ATOS, and other text analysis tools, rated five types of reference texts. The study encompassed quantitative, qualitative, and reader-task considerations, each of which is important for matching students with appropriate texts given their interests, motivation, and prior knowledge. The research concluded that ATOS is reliable and highly correlates with grade level and student performance measures.

"Common Core State Standards emphasize the ability of students to independently read and comprehend complex text," said Glenn R. James, Renaissance Learning Chief Executive Officer. "ATOS is the result of intensive research that sought to develop an accurate, quantitative readability formula. As an organization dedicated to advancing K12 education, Renaissance Learning voluntarily submitted ATOS to this independent evaluation. The results clearly indicate that educators who use ATOS can be assured it meets new standards for measures of text complexity."

Renaissance Learning provides ATOS as a free text readability tool, available in an easy to use format for educators, parents, and students. ATOS includes two formulas: ATOS for Text, which can be applied to virtually any text, and ATOS for Books. Anyone may scan text using the ATOS Analyzer. AR BookFinder, a free, web-based book-searching tool, available to everyone at, enables users to search for books based on interest, maturity, and ATOS levels. In addition, the company offers a variety of resources on Text Complexity and the Common Core State Standards at