Readability Scores on Kids’ Books Are Bogus

Most books come with an indication of how hard they are, and those estimates are mostly wrong

kids books
Image: Denise Krebs Denise Krebs

Everybody wants their kids to read—but choosing the right book, at the right level, that somehow still appeals to a kid, can be tricky. Parents want something that their children can get through, but that challenges them a little. Thankfully, most books come labeled with reading ages—estimates derived from “readability formulas” that determine how hard a book is. The problem is that most of those formulas don’t actually work.

In a new paper from North Carolina State University, researchers examined eight different readability formulas. First, they asked 360 students from first to fifth grade to read six passages out loud. Then they compared the students' reading fluency—a good indication of hard they found the text—with the readability score the eight different formulas provided. What they found was that almost every time, the readability score was inaccurate. Seven out of the eight formulas were less than 49 percent accurate, and one of them was right only 17 percent of the time.

“Overall, this work shows that teachers and parents should be very cautious about using readability levels when giving reading assignments to students,” lead researcher John Begeny said in the NC State press release. Next time you see the age level on a book, it might be worth having your kid try to read it out loud before you throw it in the cart.

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