Written by Dr. Gary Moss

This is a question I hear on occasion from students and their parents.  I hear comments such as “I worked hard to prepare for that SAT, why did my verbal score go down 30 points”.  “Or, I did a lot of practice ACTs, why did my science score go down a point.”

The answer to all questions like these has to do with the very nature of standardized tests.  Every SAT is comparable, but different from every other.  The same goes for the ACT.  Both tests represent a sampling of what a student can do on that test.  So, just like every other sample, the results are going to have a natural fluctuation. Statisticians use the phrase “standard error” when referring to this variability in scores.

For example: for the SAT math test, the “standard error” is about 30 points.  This means that if a student took the test 40 times on the same day (hypothetically, of course)  2/3 of his or her scores would fall within a 60 point band.  The distance between the high and low score would average around 120 points (on the same day!!).  That represents a lot of uncertainty about any test on any given day.

For the ACT the standard error is a little over 1 point for each of the 4 tests (English, math, reading, and science) and a little under one point for the composite (average) score.  That means the range of scores (distance between high and low score) for 40 hypothetical tries on the ACT would be over 4 points on each subtest and about 4 points for the composite score.  If you look carefully at the score results, you will see these “bands” represented around the percentile scores on the report.

So, why do scores sometimes go down? Instead of imagining 1 student taking the test 40 times on the same day, imagine the scores of 40 students.  One third are going to get a score that is either a little unusually high or unusually low (30 points on the SAT, 1 point on the ACT).  One student, however, is going to get a score that is at least 2 points over their hypothetical average score.  And, of course, one student is going to get an ACT score more than 2 points below their hypothetical average (More than 60 points below their average score on an SAT (either math or verbal).  The effects of good coaching for the ACT are about 2 points.  For the SAT math test the effects vary greatly by the length of time a student prepares, but for 2 months of preparation, the typical gain is about 60 points (less on the verbal).  So, for at least one student out of forty, the effects of coaching are going to “washed out” by the standard error within the test.

Conclusion:  It pays to take the test more than once.  If you keep preparing and take the test several times, you will most likely see your score go up at least one time.