Library Media Services

MCAS uses multiple programs to determine a student's instructional reading level. Read180 and SRI provide students with a Lexile: STAReader and AR use ATOS. ATOS and Lexiles use different mathematical formulas to determine text readability.

Readability formulas provide an estimate of a book's difficulty based on selected variables in the text, but DO NOT analyze the suitability of the content or the literary merit for individual readers. The school librarian and classroom teacher can assist the student in selecting a book that is just right. 

• ATOS - uses the number of characters in a word, the number of words in a sentence, the average grade level of the words in the book and the full text of the book. Renaissance Place also identifies books appropriate for lower grades (LG) middle grades (MG) and upper grades (UG).

• Lexiles - uses word frequency and sentence length within 100 word passages to determine text readability. Lexilies do not identify books appropriate to student grade level.

A readability index is a good starting point for book-selection process. Other factors also affect the relationship between a reader and a book including content, the age and interests of the reader and the design of the actual book. Students who are interested in reading about a specific topic, therefore motivated, are able to read text at a higher level than would be predicted by a readability index.