This information is from https://www.renaissance.com/edwords/lexile-measure/.
For more information visit https://lexile.com/.
What is Lexile® Measure?
The Lexile® Framework for Reading is a scientific approach to measuring reading ability and the text complexity of reading materials. The Lexile scale is like a thermometer, except rather than measuring temperature, it measures a text's complexity and a reader's skill level.
When these two measures match, a targeted reading experience occurs. Students who read at the right levels experience more reading achievement and growth.
How can Lexile measures guide students to appropriate books and articles?
The Lexile Framework assesses both sides of reading development: the reader and the material being read. When a student chooses texts 100L below to 50L above his or her reported Lexile reader measure, a targeted reading experience can occur. The Lexile reader measure describes an individual’s reading ability. The Lexile text measure describes the semantic and syntactic features of a book, article, or text. Both Lexile reader measures and Lexile text measures are reported on the Lexile scale and are represented by a number followed by the letter “L” (i.e., 1000L).
Lexile measures are quantitative measures that provide insights into the difficulty of the words in a book or article. It is, however, only one of three components associated with text complexity. The other two are qualitative measures (i.e., content, themes, and maturity level) and reader/task considerations.
Lexile measures do NOT measure age appropriateness, the book quality, the book's theme, or other characteristics of the book. For example, The Grapes of Wrath is a rather simple read, but it may have a theme that is inappropriate for a certain age group.
Teachers, librarians, and parents may want to consider all three components when matching students with books.
Lexile measures are valid, reliable measures of text complexity that provide a basis for matching students to reading materials. As with all readability formulas, the resulting value is an estimate of the text’s understandability.