Norms and Percentiles calculation and Interpretation

The formula for calculating percentiles is given as:

B / T * 100 = percentile

T = Total number of test-takers

B = Number of test-takers whose score are at/below a given score

easyCBM tests are largely norm-referenced fundamental skills assessments. Thus, a student’s performance is compared to national norms––scores based on a large nationally-representative group of same-grade students on the same assessment. Our norm-referenced scores are reported in raw totals, but also, in percentiles (1-100). So, for these assessments, think of baby growth charts, where children’s weight and height are compared to one another. Just like those charts, a student’s percentile rank for norm-referenced assessments compares their performance to other grade-level peers.

For most easyCBM test forms, we calculate a percentile for every possible score (within reason…i.e., for oral/passage reading fluency, once we get to 99th percentile, for a given raw score, there is no need to keep calculating additional percentiles for higher scores) using that basic formula for students included in the norming sample (see https://help.easycbm.com/how-were-norms-for-the-benchmark-and-progress-monitoring-assessments-calculated/ for more information on the norming process). These are the percentiles you see reported in student reports and in the Detailed Percentiles Table or the Progress Monitoring Scoring Guidelines available on the Reports page after logging into your account.

So, for example, a perfect 20/20 on the Grade 3 Winter Benchmark in Vocabulary is represented by the 87th percentile in reporting because, in the norming sample, 87% of students scored below 20/20 on the Grade 3 Winter Benchmark in Vocabulary. Or, in other words, 13% of students in the norming sample scored 20/20 on that measure.

The norms are based on the grade level of the measures - and performance of students at that grade level on those measures.

So, if your 7th grade student scores at the 50th percentile on a 5th grade measure, they performed as well as an "average" 5th grader taking that measure at that time of the year.

To interpret student performance on the easyCBM measures, one compares a student's raw score on a given measure to the percentile rank associated with that score.

This information can be found by comparing the student's score to the percentile rank lines on the individual student report graphs, by hovering over a raw score in the Benchmark Report table, or by referring to the PDF “Interpreting Progress Monitoring Scores” and the Detailed Percentiles chart. In all cases, this information gives an indication of how a student is performing relative to the performance of other students on that measure at that point in time.

Performance at the 50th percentile rank can roughly be interpreted as 'average' performance for students in that grade on that measure at that point in time. Performance below the 50th percentile rank indicates that a student is performing below average on that measure at that point in time, with lower scores indicating performance further below average grade level performance.