Q. How do I compute the percentile score for my child’s standardized achievement test? Is it an average or do some parts have more weight?

A. A standardized achievement test is not like the subject tests you give during the year. Parents don’t have the information that is needed to compute a percentile score. The test must be returned to the test supplier to be scored.

Your student’s test scores are compared to a national reference group called a “norm.” The “norm” is made up of a group of students across the nation who took the same test in the same grade level. This is called the norm group. Because parents don’t have the achievement test “norms” to use for this comparison, you cannot compute the percentile score for your student.

A percentile rank shows the percentage of the norm group that has scores equal to or less than your student’s score. It doesn’t measure the percentage of questions answered correctly or give an average. The percentile compares your student’s scores to the norm group’s scores.

The number of items the student answered correctly is called the “raw score,” but it has little meaning alone. A raw score must be compared to the norm group in order to determine a percentile score. The 50 percentile is considered average. A percentile rank of 80 means the student scored better than 80 out of 100 students in the norm group; 20 students scored as well or better than your student. It doesn’t mean the student got 80 out of 100 items correct or that he answered 80% of the questions correctly.

Homeschool parents must send the original score sheet back to the publisher or the test supplier for scoring. They have the formulas to provide testing results for their test. You can expect to receive the results in four to six weeks. After you receive the results in the mail, send a photocopy to your division superintendent by August 1 each year. The composite score must be in or above the fourth stanine (23 percentile or higher) in order for you to continue homeschooling.

Reminder: Homeschoolers who have complied with the homeschool statute are required to provide a composite score only. A composite score is composed of the language arts and mathematics sections including subtests. Homeschoolers are not required to take the science and history portions of the test.


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  1. Mark D. Otley says:

    Not “equal to or less than”, just “less than”. One can never get a percentile of 100 — the highest is 99.

    If enough members of the norm group got a perfect score, one might not even be able to get a 99. On very short sections of multi-part tests, I’ve gotten a percentile in the 80s with a perfect raw score.