Standard Bell Curve

 Standard Bell Curve

This month we are talking all about Evaluations, understanding Evaluations, and using those test scores!


This week we have a visual that helps to explain the bell curve of performance for Standardized Test Scores. It can be really difficult to visualize what these scores mean and so this is a great way to be able to show parents, teachers, or other interventionists how a student is performing in any given domain. If you missed our more in-depth post about how to interpret Evaluation Data check out our blog here!


This visual is awesome because it explains what a bell curve is in addition to what standard scores and percentiles are. So as a review or in case this is new:

What is a Bell Curve?

The standard bell curve is a visual of a "normal distribution" of performance. Normal distribution means that students across the nation were given an assessment and the scores were averaged out. The majority of students fall right at the average. However, a percentage of students are scoring higher than average and a percentage of students are scoring lower. The normal curve assumes that the same amount of people scored higher than the average as scored lower than the average at a predictable interval.

What are Standard Scores?

Standard scores are the most common unit of measurement using the normal distribution. We use Standard Scores to measure student performance to determine how students are performing in comparison to their peers across the nation. Standard Scores have been statistically calculated such that the average test score is 100. The average "deviation or variation off of the average is 15 points. This means that scores between 85-115 statistically fall within what's considered "average".

What are Percentiles?

Percentiles are based off the standard bell curve and give an idea of a child's performance relative to the national average. If a student performs at the 75th percentile on a test, out of 100 students he or she would perform better than 74, putting him or her in the upper quartile of test performers. If he or she scores in the 25th percentile, he or she performed better than 24 out of 100 placing him or her in the lower quartile of performance.

We will be diving into specific tests that are often used or can be used to give you more information on how a student is doing with each of the listed skills next week, so stay tuned!


This printable will only be available for 1 WEEK.  To download, click here

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