What is Readability?

Three pupils looking at books by Marcus Tolsta

In an ideal world, we wouldn't need readability scores. We would have unlimited time to read children's literature, enabling us to recommend just the right book every time to turn reluctant readers into enthusiastic ones. The reality is that it's very useful to have some indication of how linguistically challenging a book is likely to be, even if the science isn't perfect.

So what are readability scores, and which one should you use? How are they calculated, and are they useful and reliable? Let's take a look at a few examples.

Flesch Kincaid Readability Test

The Flesch Kincaid readability formula gives you two different scores. One is for Reading Ease - this is a score from 1 to 100 indicating (you guessed it) how easy a document is to read. The other score is Grade Level - this indicates which grade you would need to be studying in order to understand the text (it refers to the US grade system).

You might be familiar with this one because it can be calculated from within Microsoft Word (even in Word 2003 and older).

The Flesch Kincaid scores are calculated using an algorithm which considers sentence length and also word length in syllables. The major flaw with this is that even if a word has a higher number of syllables, this is not a reliable indicator of difficulty: for instance, the word 'remember' is more familiar to younger children than the word ''tawdry', but under this system it is treated as the more difficult word.

It's unlikely you'll be able to apply this test to a print book; however, if you've got an ebook you will sometimes be able to copy and paste a section of text into Word so you can test it. It might be slightly easier to apply the Coleman Liau system to print books (see below).

Coleman Liau Index

Coleman Liau tends to appear on predominantly US books, but it's included here because of its approach to calculating readability. Like Flesch Kincaid, it considers length of sentences; however, it considers the amount of letters in words rather than the amount of syllables. Its creators say that this is better and that "there is no need to estimate syllables since word length in letters is a better predictor of readability than word length in syllables". If you agree, you can calculate the readability of your document according to this index using this online calculator, which includes Coleman Liau, Flesch Kincaid and some other scoring systems. 

ATOS Readability Formula

This is the score used in the Accelerated Reader software by Renaissance Learning. If you're not familiar with the Accelerated Reader program, it's a system which aims to improve children's reading by getting them to read progressively more challenging books. The software assigns them a Reading Level based on a short test, and after this they can choose books to read using their Reading Level as an indication of whether they will understand and enjoy the book. You can find books using the Accelerated Reader online database.

The ATOS formula has a notable advantage over the previous two systems: it bases its score on the entire text of a book and not just a small selection. The Accelerated Reader program also lists an 'interest level' for a book, indicating what age group the content is likely to appeal to. This is useful if you have older pupils who are reading below their expected level - you can make sure they pick books which they will be able to read with content which is likely to pique their interest. The same applies for younger readers who are reading beyond their expected level. The interest level of each book on the database is determined by publishers and the professionals at Renaissance Learning.

Renaissance themselves are quick to point out that any readability score doesn't tell the whole story. Also, the tests they use to determine if a pupil has read and understood a book are very much focused on recall of plot points rather than higher order understanding. However, Renaissance are at pains to point out that these tests are not supposed to do the job of a teacher in cultivating a higher order understanding of a book.


What other factors affect readability?

The first consideration has to be line length. Whatever medium you're reading on, documents with more than 13 words per line are more difficult to take in. This is because the eye, having gone so far to the right of a page, can struggle to go back to the left and locate the next line: often it will accidentally skip two lines ahead. We can read quickest when presented with less than 13 words per line, so publishers always typeset their books with this in mind. 

Line spacing is another factor to consider. Lines spaced 1.5 pt apart are easy to read, and books for young children are often spaced with at least this amount between the lines. 

The type of font you should use depends on whether you are using print or digital platforms. On print, serif fonts (like Times New Roman) are easier to read because they have small feet which guide the eye towards the next letter. On a screen, sans serif fonts like Arial and Helvetica work best because simpler shapes are more readable than complex ones when backlit, and since sans serif letters don't have feet they are less complex shapes than serif letters. 

Can I use Comic Sans?

(Sigh.) If you are attached to this insatiably saccharine font then you can use it for digital stuff - presentations and the like. But on worksheets stick to serif fonts. Courier New is noted for being easy for people with dyslexia to read, as the letters are well spaced out.

The bottom line is that readability scores are probably necessary, and they make progress tangible as children attempt texts with higher scores. The first port of call for me is always a librarian, teacher or one of my colleagues when I'm looking for book recommendations: there's no substitute for the expertise of a human being. On that note, remember it's National Libraries Day on February 7 - why not take your pupils into a library and consult your local librarian for their expert recommendations?

There are lots of readability calculations we haven't covered here, including Lexile Scores - which ones work for you? Do you believe they're helpful? Let us know in the comments below.