The SAT, Test Prep, Income and Race

Alex Tabarrok:

All of this is almost entirely at variance with three facts, all of which are well known among education researchers.

First, test prep has only a modest effect on test scores, on the order of 20-40 points combined for a commercial test preparation service. More expensive services such as a private tutor are towards the high of this range, cheaper sources such as a high-school course towards the lower. Buchmann et al., for example, estimate that private tutors increase scores by 37 points while a high school course increases scores by 26 points.

The average SAT score among those with a family income of $20,000-$40,000 is 1402 while the average score among those with an income $100,000 higher, $120,000-$140,000, is 1581 for a 179 point difference. Even if every rich family had a private tutor and none of the poor families had any test prep whatsoever, test prep would explain only 20% of the difference 37/179. If rich families rely on tutors and poor families rely on high school courses, the difference in test prep would explain only 6% (11/179) of the difference in score.

The second surprising fact about test prep is that it doesn’t vary nearly as much by income as people imagine. In fact, some studies find no effect of income on test prep use while others find a positive but modest effect. The latter study finding (what I call) a modest effect finds that in their sample a 2-standard deviation increase in income above the mean increases the probability of using a private test prep course less than whether “Parent encouraged student to prep for SAT (yes or no).”