Updated: Apr 29, 2019
Hello! I wanted to share some information with you about how Lexile scores are determined. I've been getting a lot of questions this year about what Lexile scores mean for those students that may be in need of intervention so I hope this helps clarify things a bit.
First, it is important to understand that the Lexile score algorithm chiefly analyzes both the word and sentence complexity of a text. The difference between a third grade book and an eighth grade book may be easy to distinguish based on the length and complexity of the sentences as well as the word choice and even any non-literal use of language in a text. The longer the words and the more complex the sentences, the more details and the more depth a text may contain, and therefore a higher Lexile score assigned to that text. The challenge is when teachers and parents begin discussing grade-level equivalency of a text, especially between grade levels closer together, that concerns and confusion can often arise.
The first thing to notice is that Lexile scores do not start and stop according to grade levels. A "grade-level equivalency" for a Lexile score is designed to account for (1) changes from beginning through the middle and to the end of a school year, and (2) percentiles that overlap across grade levels. See the image below for ranges that account for Lexile scores between the 25th and 75th percentile during the middle of a particular school year.
For example, a student in fifth grade that receives a Lexile score of 960 is closer to the 75th percentile for that grade level. This means that nearly 75% of other students in that grade level are likely reading texts at a lower Lexile score. This also means that a little more than 25% of students in fifth grade are likely reading texts at a higher Lexile score. The important takeaway here is that this fifth-grade student with a Lexile score of 960 is a strong reader at the fifth grade level. Texts designed with word and sentence complexity that result in a Lexile score of 960 are appropriate for strong readers at the fifth-grade level.
If that same student is still reading at a Lexile score of 960 halfway through sixth grade, these ranges would put that student closer to around the 40th percentile of sixth grade students. This would mean that about 60% of other students in that grade level are likely reading texts at a higher Lexile score. Again, texts designed with word and sentence complexity that result in a Lexile score of 960 are still appropriate for this student but might struggle with texts in a textbook that might be designed for sixth-grade students closer to the 75th percentile at the sixth-grade level.
To take this one step further, when this same student enters seventh grade and is still reading texts at a Lexile score of 960, this student might be considered near the 25th percentile of seventh-grade readers. This would mean that nearly 75% of students in seventh grade may likely be expected to read texts at a much higher Lexile score. Texts designed with word and sentence complexity that result in a Lexile score of 960 will still be appropriate for this student but they'll likely struggle with texts in a textbook designed for seventh-grade students closer to the 75th percentile at the seventh-grade level.
Please note that these ranges are not guarantees but rather used as a guide for measuring growth according to general text complexity expectations for specific grade levels.
The reason these Lexile ranges overlap is because the Lexile algorithm analyzes word and sentence complexity of texts - not students. This means a seventh-grader with a 960 Lexile may be considered a weak reader in need of intervention, while a fifth-grader with the same Lexile score may be considered a strong reader.
In the case of a fifth-grade student reading texts that fall below a Lexile score of 760, there is a chance that the student may not be fully prepared to promote to sixth grade without targeted intervention in place at the start of that next school year. It is important that students receive specific intervention that target areas related to reading such as sentence structure and word analysis as well as context and comprehension.
A standards-based approach would help account for the specific standards that address each of these related skills and help teachers and students focus their time and attention in an intervention setting on the most critical areas of need.
I hope this information helps clarify how to use Lexile scores to assist in more accurately determining student reading growth and proficiency.