Identifying the reading level and challenge of a book

Readability formulas are helpful tools used by teachers and librarians to match pupils with appropriate books. Today’s teachers/educators have many different formulas from which to choose. All readability formulas work by counting the variables that have the biggest impact on readers being able to ‘take in’ a bit of writing: sentence length, number of syllables per words, number of passive sentences.  Each formula works things out in a slightly different way. This is a brief summary of some of the more common ones used to identify the readability of children's fiction.

Flesch-Kincaid reading ease

The Flesch-Kincaid reading ease score is the most widely used readability checker. 

It gives you two scores. A regular number, on a scale of 1 to 120 (higher is better). And a grade that shows what American school year you’d need to be at to understand it (American schools are a year behind the English system – so a fourth grade score on one of these tests means year five in the UK).

The DFE have published details of Flesch-Kincaid scores of the texts used in the 2016 KS 2 SAT, suggesting that The Lost Queen was 3.7, Wild Ride was 3.6 and The Way of the Dodo was 4.9. The overall level of the test according to the DfE was 4.1 They also provide details of an online analyzer that can be used to identify the scores of extracts. Flesch-Kincaid is not designed to analyze whole books.

                  The Lexile framework

The Lexile Framework for Reading, developed by MetaMetrics, uses one scale to provide measurements of both the difficulty of a particular piece of text and the comprehension level of a particular reader.  The Lexile Scale typically ranges from 200L to 1700L, though scores may occasionally fall below and above that range.  200L is considered beginning reading level.  1200L is considered workplace-level text.

The Lexile score for a piece of text is determined by two factors:

1. Word Frequency

  • How often are commonly-used words used?

  • Based on a corpus of hundreds of millions of words used in a variety of contexts

  • Takes into account the likelihood that a reader will have had previous contact with the words used

2. Sentence Length

  • Based on the number of words per sentence


Both non-fiction and fiction prose can be accurately Lexiled; poetry, free-form writing, and outlines are among the types of writing that cannot be accurately Lexiled due to their lack of sentence structure. A Spanish version of the Lexile Framework is also available.

The database, available to all at, contains information on tens of thousands of books and articles, with more being added regularly.  The Lexile database can be searched using Lexile score, title, author, and key words.  Using this database, a teacher can identify a list of books about the same topic or by the same author but that represent a variety of reading levels that can be matched to his or her pupils. 

Metametrics have carried out an analysis of the UK reading SATs for both KS 1 and KS 2 and found that the 2016 lexile levels were as follows

AD: Adult Directed 
Picture books are frequently considered for an AD or "adult directed" code because they are usually read to a child, rather than a child reading them independently. This is the classic example of parent and child sitting together on the couch with the book open in their laps. Although seemingly easy reading, picture books can still present a challenging independent reading experience to an age-appropriate reader for reasons of text difficulty and book layout or design.

The text difficulty of picture books varies widely across the genre. For instance, Maurice Sendak's Where the Wild Things Are(HarperCollins Publishers) is a beloved read-aloud for preschoolers. Its Lexile measure of 740L, however, is around the average reading ability for someone ending fourth grade. Upon a closer look, the text comprises long sentences and contains some fairly high-level vocabulary such as "mischief," "private," "gnash," and "rumpus." The parent on the couch would help the preschooler sound these words out and decipher these long sentences. Therefore the book is coded adult directed and the measure is AD740L.

                                ATOS readability                                        formula for books


In 2000, researchers of the School Renaissance Institute and Touchstone Applied Science Associates published their Advantage-TASA Open Standard (ATOS) Reading ease Formula for Books. They worked on a formula that was easy to use and that could be used with any texts.

The project was one of the widest reading ease projects ever. The developers of the formula used 650 normed reading texts, 474 million words from all the text in 28,000 books read by students. The project also used the reading records of more than 30,000 who read and were tested on 950,000 books.

They found that three variables give the most reliable measure of text reading ease:

  • words per sentence

  • average grade level of words

  • characters per word

All the books in their database have an ATOS book level. ATOS book levels are assigned using the ATOS readability formula. For example, a book level of 4.5 means that the text could likely be read independently by a student whose reading skills are at the level of a typical fourth-grade student during the fifth month of school. Again they equate to US grade so in the UK we need to add 1 to get the equivalent year group. So, a book level of 4.5 translates as the 5th month of year 5.

Their extensive database  is freely available to access and like lexile there is also a free online analyzer enabling teachers to analyse other texts such as newspaper articles.

Book Banding


Book Banding is a national scheme that grades children’s reading books according to the difficulty of the text. Each level of books is given a colour. When a child is learning to read, it is important that they have access to lots of different kinds of books and a wide vocabulary. Most reading schemes have their own core vocabulary and many teachers have found that children struggle when they are asked to read something different. Book Banding is designed to help schools grade their reading books across different reading schemes. Book banding enables you to provide access to books from different reading schemes within each book band so that children have access to the variety they need whilst still being supported at the right reading level. All publishers grade their scheme to their specifications but the Book Band scheme is far broader in its levelling. It is based on careful research into the kinds of words used in each book, the length of the sentences, punctuation, story style or non-fiction format and text size. It also supports a progression of reading strategies.

Comparison of the Different Systems

Click on the link for a chart which compares each of the different measures. I have also included reading recovery and ORT. This hopefully will help teachers place books within the appropriate book band/level and make informed choices about the texts they choose to use a class novels and with small groups to ensure that they are providing the right level of challenge.