Comparing Lexile Measures and Grade Levels

Common Issues With Grade Equivalents

Grade equivalents are scores based on the performance of students in the test’s norming group. The grade equivalent represents the grade level and month of the typical (median) score for students. For example, a fifth grade student who earns a 5.9 on a norm-referenced test has earned a score similar to the 50th percentile students in the test’s norming group who were in their ninth month of fifth grade.

There are a few issues with grade equivalents:

Grade equivalent scores are often misinterpreted as being a grade level standard. A grade equivalent of 5.9, for example, does not necessarily represent the desired level of achievement for all grade 5 students at the end of the school year. It simply represents the norming group’s median score, or projected score at that point in time. Achieving the same score as the average student in the norming group may not be an appropriate goal for all students. In contrast, Lexile measures are not generated from grade level norms and do not presume a specific grade level interpretation. Struggling students are not stigmatized with a grade equivalent that labels them as “below grade.” Rather, students have an independent Lexile measure and can select appropriately difficult books within their Lexile range.

The grade equivalent does not represent the appropriate grade placement for a student or the level of the material the student should be studying. Imagine a student scores a 7.9 on a fourth grade reading test. The 7.9 does not mean that she’s mastered seventh grade reading material or that she should be reading books appropriate for seventh or eighth grade students. All you know for sure is that the student scored well above the average seventh grade student in the norming group in reading. Because the Lexile measure does not suggest grade level placement, this type of misinterpretation does not occur. The Lexile measure can be used to identify material at the appropriate difficulty level for the student regardless of the student’s grade level.

Measuring Growth

In addition to potential misinterpretation, the grade equivalent scale makes it more difficult to measure growth. The grade equivalent scale is not a scale of equal intervals. This leads to the common misperception that a student who moves the same number of grade equivalents at one level on the scale (such as from 2.5 to 2.9) has “grown” the same amount as a student who moves the same number of grade equivalents at a different level on the scale (such as from 8.5 to 8.9). The amount of growth in ability needed to move from 2.5 to 2.9 is much greater than the amount required to move from 8.5 to 8.9.

Because the Lexile scale is an equal interval scale, the amount of growth in ability required to move between two points is the same at every point on the scale. Moving from 240L to 340L on the Lexile scale represents the same increase in ability as moving from 840L to 940L. Because Lexile measures are equal interval units, they can be used in mathematical calculations.