To Lexile or Not to Lexile, That is the Question

  • Lexiles
  • 18 October, 2015

Teacher question:

Our school district is going wild over Lexiles because they are in the Common Core standards. I think they are overdoing it and don’t feel comfortable with some of the decisions that we are making. What are the weaknesses of Lexiles?

Shanahan response:
First, Lexiles is only one of several readability measures included in the CCSS. They started with that one, but as studies were completed they added ATOS, SourceRater, and several others.
Everyone has to remember that Lexiles (and any readability measure) is a prediction of difficulty, and there since it is a prediction there will be a certain amount of error in it. It will sometimes overestimate or underestimate the difficulty of a text. It does this because it predicts difficulty on the basis of only two variables (word difficulty and sentence difficulty). 
Obviously there is more to text difficulty than that. Nevertheless, the predictions tend to be reasonably accurate. Why?  Mainly because of the consistency of authors. If an author uses simple words and sentences, he/she will probably organize their writing in straightforward ways, and the cohesive structure, tone, and so on will probably not be particularly nuanced or complex. 
But that isn’t always the case. Hemingway tended to use an Anglo-Saxon vocabulary, and are there any shorter sentences in the English language?, but try to keep track of who is speaking across pages of dialogue or to grasp what the characters are feeling just on the basis of the words themselves… Good luck, 5th graders.
As I say, Lexiles can mispredict. 
The appendices to the Common Core recommend some good ways of looking at text to adjust their placements up or down a bit. Thus, Lexiles (and the other estimates) can get you close, but then you need to use some judgment. No matter what Lexiles predicts, what do you think about using this text with a bunch of kids? (And remember, readability is only one part of the text selection equation—having kids read about sex or violence or racism, etc. in school may be just as problematic if the texts are easy or difficult).
Another reason the predictions aren’t perfect has to do with the reader. The idea of Lexiles and the other formulas is that we are trying to predict readers’ comprehension, and there can be reasons from a reader’s side of the equation why a text may turn out to be easy or hard. Let’s face it, if the author and I share a lot of knowledge in common, I’ll be able to bridge the gaps that he/she leaves for me. However, If the reader has less of a grasp of the content than the author assumed, then the sledding will be a lot tougher. (Yes, it doesn’t matter if there isn’t much shared knowledge if the writer doesn’t presume such information in the writing.)  
That means when you are selecting materials you have to think about what the kids might know and whether this text addresses the topic appropriately or not. Again, separate from the complexity of language: does the text over-explain something kids will already know (boring) or under-explain new topics in clear language leaving the kids confused?
Another thing to understand is that a readability score for a text is just an average. The average will be more accurate the longer the text is (more data, greater reliability). However, many teachers and publishers will estimate the difficulty of a text, but then will have the kids read a particular chapter from that text. Different sections of a text may vary quite a bit (so the overall difficulty for a text may be 5th grade, but the chapter you are actually teaching is 3rd grade or 8th grade difficulty).
It might be a good idea to run Lexiles on the actual excerpts and not to trust that the excerpt is a good representation of the overall text.
Readability measures can be very useful predictors of difficulty, but they do not help one to write or rewrite texts for particular audiences. For example, someone might select a text that they want to use, then they find out that according to Lexiles, the text is too easy or hard for the intended purpose. What to do? It is not uncommon that teachers or publishers adjust the passage, perhaps by replacing some words or breaking up a few sentences, etc. That will change the score (making the text appear to be more suitable), but it rarely improves the situation. It should be easy to not do this one yourself, but keeping publishers from playing such games is a bigger challenge.
Like your district, I’m a Lexile fan, but that doesn’t mean that we should misuse or abuse Lexiles. It is just a tool, and one that can solve problems or create problems. Let's not create them.


See what others have to say about this topic.

Tracey Flint Jun 12, 2017 07:54 PM


As a secondary teacher of Reading and English, I agree that we have to be cautionary with Lexile measures. Our literacy staff development makes the point to instruct teachers to look at a number of different factors when selecting texts for classroom or assessment use.

The Appendices in the Common Core Standards for ELA have great resources about looking at qualitative measures also. I also highly recommend the resources provided from Achieve the and EngageNY. Both have some quality examples of templates and exemplars of how to quantitatively AND qualitatively evaluate a text for classroom use.

Also, recently, MetaMetrics (for all the Lexile geeks out there)has introduced Lexile by Chapter Guides, providing individual Lexiles for chapters of commonly taught texts.

Timothy Shanahan Jun 12, 2017 07:55 PM


I agree with all of these suggestions. However (and I know I'm pushing back both against what you have written here and what I wrote in the original post), the Lexile levels can be wrong, but their level of accuracy is quite good. So while it is imperative that teachers both be cautious in their acceptance of the Lexile levels, they also need to be cautious in assuming that the levels will usually be wrong. In fact, Lexile levels can explain about 70% of the variance in reading comprehension which means they are right a lot more than they are wrong. If you find yourself over-ruling the Lexile determinations a lot, then you are probably overdoing it. Thanks, Tracey. Good resources.

Ben Rogers Jun 12, 2017 07:55 PM


Using the Lexile score as a predictor of how challenging a reader will find a text, rather than a simple measure of the text, is really useful - thanks.

Do you know if the variance for difficulty in subject specific texts is also around 70%? I'm a science teacher.



Timothy Shanahan Jun 12, 2017 07:56 PM


Lexiles lumps all texts together, including science texts. There is another scheme, SourceRater, that has two different prediction formulas: one for literature and one for informational texts such as science. They claim to get a more accurate prediction that way, though overall their prediction levels seem to be quite similar to Lexiles. I definitely would feel comfortable using either approach with science materials--with the cautions already recommended.

Timothy Shanahan Jun 12, 2017 07:57 PM


I received the following from Malbert Smith, one of the creators of Lexiles. He points out a study recently conducted by he and his colleagues showing what I claimed in the above blog entry: Lexiles for a chapter can be quite different from Lexiles from an entire book.

"Enjoyed reading your post today (as I always do) on “To Lexile or Not to Lexile”. I have written a piece (attached) that very much supports your claim. If you feel it is appropriate please feel free to post or publish. We have a new section on our web site that contains many of the canonical classics that everyone has to read.

Malbert Smith Study of To Kill a Mockingbird

Sara Jun 12, 2017 07:58 PM


I notice that you also use the variance for oral fluency in your other post. Would you mind sharing the source of variance for Lexile and Oral fluency?


Timothy Shanahan Jun 12, 2017 07:58 PM


The source of the variance for oral fluency is based on several studies that have, over the years, reported correlations between oral reading and reading comprehension. There are many such studies. One calculates amount of variance explanation between two variables by squaring the correlation. Thus, if the correlation between oral reading and reading comprehension is about .92 as it often is in second-grade, then you end up with approximately .85 variance explanation.

The Lexile numbers come from the men who created Lexile (personal report). It is likely in some of the technical reports on the MetaMetric website. The 70% variance explanation was unheard of for a readability formula when they first designed Lexile, but now I see that some of the other newer measures also have this level of prediction power (such as ETS's Source Rater). However, that 70% is somewhat inflated because it looks at the power of Lexiles across many grade levels; a comparable analysis looking at a single grade level would result in much lower variance explanation (and that's true for the alternative measures as well).

Sara Jun 12, 2017 07:59 PM



Lisa Seeley Jun 12, 2017 08:00 PM


I was shocked to read that a school had gone overboard with something because it related to CCSS.....ha! NOT! Unfortunately, that seems to be a common trait among many schools, who in their quest to align with mandates and recommendations sometimes jump the gun or take things too far. I would say that my school is among the many Lexile obsessed schools as well. I teach a remedial reading program that focuses heavily on Lexile measures- students take a reading inventory and are given their Lexile level that dictates much of what they do in the program. Sometimes I feel like we are treating them like prisoners at Auschwitz, stamping their identity on their arms, lest they forget they are struggling readers. On the other hand, when I am able to provide a struggling reader books that are challenging and just outside of their Lexile range, while not quite at frustration level, I don't mind Lexiles as much.

I would have to agree with you when you remind us that Lexile levels can solve problems or create them. That is great advice! Lexile levels can give us a great idea of what books would be a good fit instructionally for our students, but they should not be used against a student. I can't stand it when a child is told they are not allowed to read something because it isn't in their Lexile range. While I agree with the practice of providing books in a child's instructional range, if they have their heart set on reading "The Hunger Games" and it is above or below their Lexile range....I don't care! Motivation and interest goes a long way in student reading success. A student who WANTS to read a book that isn't in their Lexile range will likely do better with it than a student reading a book in their Lexile range that they are not interested in.
Just like anything in life, we need to practice moderation when it comes to using Lexile levels. They have the potential to be a very useful tool in literacy instruction, but we need to make sure we aren't replacing common sense and good teaching practices with strict rules based on a single measurement that is not fool proof.
Thanks so much for your insight on this!

Timothy Shanahan Jun 12, 2017 08:00 PM


I agree with you Lisa, but am surprised that anyone thinks that is what Common Core recommends, encourages, or supports the idea of teaching kids at their Lexile levels. Any school that is doing that because of Common Core is clearly lost. The big innovation of CCSS is to teach kids at Lexile levels that are high enough to get kids to be college and career ready--you won't get there teaching kids at their levels if they are behind (as your students are). Crazy.

Lisa Seeley Jun 12, 2017 08:00 PM


The goal is to scaffold them of course, to get them to grade level. The idea is to have them working at and just above their Lexile range while constantly pushing that range up as students are successful in order to increase their Lexile and ultimately get where they should be. I have no issues with this concept, only with the practice of being so strict about not letting students choose books not in their range.
Thanks for responding!

Sarah Jun 12, 2017 08:01 PM


Hi Dr. Shanahan,

For a repeated reading intervention, would you recommend ordering passages by Lexile Level or Flesch-Kinkaid.

I noticed while analyzing passages that some passages had a lower FK level but a higher Lexile level. For example.
Passage #1 has an FK of 1.9 and a Lex level of 420L
Passage #2 has an FK of 0.3 and a Lex level of 440L

Is this due to the face that FK bases there readability off of syllables and Lex doesn't?
Any further explanation on this would be helpful!

Thanks so much!!


Timothy Shanahan Jun 12, 2017 08:01 PM


There are approximately 300 different instruments that have been developed to predict how difficult a text is likely to be. None of these works without error, but many are able to estimate text comprehensibility more accurately than most of us could do on our own. These two instruments were developed at different times (Lexiles in the 1990s, but its creators keep updating it; and F-K which was developed about 60 years ago and has not been re-normed since it appeared ~1950). They also predict different things. The F-K predicts the ordering of a set of texts presumed to be ordered by difficulty, and Lexiles predicts how well kids comprehend passages that have been Lexiled. When they disagree, my assumption is that Lexile will be more accurate for most uses, and i would simply ignore the FK.

The two measures try to predict word sophistication in different ways. F-K counts syllables since harder words tend to be longer than shorter words. Lexiles counts how many words are rare in the language, since more frequently used words tend to be easier. That may be the difference, but both of those indicators correlate with comprehension, but generally, the word frequency approach has a higher correlation with text difficulty. Go with Lexile.

Sarah Jun 12, 2017 08:02 PM


Thank you so much!!!

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To Lexile or Not to Lexile, That is the Question


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