Lexile® measures and grade levels
For many reasons, MetaMetrics does not report student ability levels as grade equivalents. Although grade equivalents are widely used in the educational community, they are a deceptively simple way to characterize a student's test score. The misconceptions about grade equivalents have been widely noted (e.g., AERA/APA/NCME, 1985; Airasian, 1994; Miller, Linn, & Gronlund, 2009; and Stiggins, 1997). The International Reading Association (IRA) crafted a resolution about the misuse of grade equivalents. In it, the IRA "strongly advocates that those who administer standardized reading tests abandon the practice of using grade equivalents to report performance of either individuals or groups of test-takers..." (IRA, 1991).
What are 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 5th-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. Normative data are often collected at one point in the year from students in two or more grades. To obtain scores for all months and for grades outside of the norming group, scores are interpolated and extrapolated from the actual student scores.
What is the difference between a Lexile measure and a grade equivalent?
There are fundamental differences between Lexile measures and grade equivalents. The Lexile measure represents a student's level on a developmental scale of reading ability—the Lexile scale. In contrast, a grade equivalent represents a student's ability level in comparison to students who were in the specific test's norming group. The Lexile measures can stand alone in their interpretation. These measures do not depend on who was in the norming sample, when the norming test administration occurred, or which testing instrument was used. A few key problems associated with grade equivalents are described below. All of these problems can be avoided by using Lexile measures.
Grade equivalent scores are often misinterpreted as being a grade level standard. A grade equivalent of 5.9, for example, does not represent the desired level of achievement for all grade 5 students. It simply represents the norming group's median score, or projected score, for 5th-grade students in their ninth month of schooling. Achieving the same score as the average student in the norming group may not be an appropriate goal for your students.
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.
MetaMetrics has studied typical Lexile ranges for students in specific grades. Educators who are interested in this type of normative comparison can find the information here .
The grade equivalent does not represent the appropriate grade placement for a student or the level of the material the student should be studying. Grade equivalent scores should never be interpreted literally, but rather as rough estimates of grade level performance. Imagine a student scores a 7.9 on a fourth-grade reading test. It should not be assumed that she has mastered 7th-grade reading material or that she should be reading books appropriate for 7th- or 8th-grade students. All that is known for sure is that this student scored well above the average 4th-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.
The grade equivalent scale is not an equal-interval scale. Grade equivalent units should not be used in mathematical calculations such as determining the mean. Grade equivalent scores are often treated as if they represent equal units. This leads to the common misperception that a student who moves the same number of grade equivalents at one level on the scale (e.g., from 2.5 to 2.9) has "grown" in ability the same amount as a student who moves the same number of grade equivalents at a different level on the scale (e.g., from 8.5 to 8.9). In fact, grade equivalent units are not equal-interval units. 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 grade equivalents are not equal interval units, they should not be used in mathematical calculations such as averaging.
The Lexile scale is an equal-interval scale. Regardless of the point on the scale, the amount of growth in ability required to move between two points is the same. In other words, moving from 240L to 340L on the Lexile scale represents the same increase in ability as moving from 840L to 940L. Lexile units can be used in mathematical calculations.
When is it appropriate to use a grade equivalent?
It is appropriate to use grade equivalents to compare a student's performance with that of the test's norming sample, which for most tests is a nationally-representative sample of students. For example, a 6th-grade student was tested in reading during May. His grade equivalent was 6.9. It can be concluded that this student is performing similarly to average students (50th percentile) in the national standardization sample.
Grade equivalents can also be used to interpret the performance of a group of students. Once the mean scale score for a group of students is calculated, it can be converted to a grade equivalent for the group as a whole. To illustrate-the mean scale score for the students in Mrs. Johnson's fourth-grade class tested during the last month of the school year was 693. When converted to a grade equivalent score, 4.9, it can be concluded that the students in Mrs. Johnson's class are reading at a level consistent with the average students in the norming sample at the end of the school year.