What’s the score on readability formulas?

School children are usually given reading assignments geared to their grade level. At least, that’s the idea. The trouble is, according to John Begeny and Diana Greene from North Carolina State University, our current methods of evaluating the ‘readability’ of texts may be seriously flawed.

A number of factors go into determining the difficulty level of reading material. The percentages of ‘easy’ words (with which kids at a particular grade level are likely to be familiar), the percentage of multisyllabic words and the average number of words per sentence all go into mathematical formulas to compute readability. Not surprisingly, the different formulas don’t all agree on the readability score of specific texts. The bigger question is whether any of them can give an accurate picture of how challenging a piece of literature is.

The authors recruited 360 students in second through fifth grade for their study. Each child was asked to read six short passages aloud, two of which were supposedly below his grade level, two at grade level and two above grade level. Oral reading ability was measured as the number of words read correctly in one minute. 

Of the eight different readability scales the authors used, most were unable to either predict actual reading difficulty or accurately discriminate between grade levels. For example, the kids didn’t necessarily find the 4th grade passages more challenging than the 3rd grade passages. 

The most successful formula in this regard was one called Dale-Chall, and even it only had a 79% track record. At best, the other seven formulas were valid for a single grade level rather than for all four tested grade levels. All the formulas were more accurate for above average readers than for below average readers, which is, of course, the demographic most in need of reading instruction. 

Where does this leave the teacher trying to either assess a student’s reading ability or select appropriately challenging reading material for her class? A teacher in this position might do better trying a few literature passages and seeing what works rather than relying on readability scores. 



John Begeny, & Diana Greene (2014). CAN READABILITY FORMULAS BE USED TO SUCCESSFULLY GAUGE DIFFICULTY OF READING MATERIALS? Psychology in the Schools, 51 (2) DOI: 10.1002/pits.21740