Joshua M. Hyman, an assistant professor of public policy at the University of Connecticut, studied the effects of this initiative while he was my student at the University of Michigan. Professor Hyman analyzed the test scores and college attendance of all public high school students in Michigan, before and after the ACT requirement.

The results were surprising. It was not just low-achieving students who had been skipping the ACT (or the SAT, which Professor Hyman also tracked). For every 1,000 students who took a college exam when it was optional, and scored high enough to attend a selective college, another 230 high scorers appeared once the test was mandatory. For low-income students, the effect was larger: For every 1,000 students who scored well on the optional test, an additional 480 did so on the mandatory test.

In this study, a score above 20 on the ACT was used to roughly capture “college readiness.” The average ACT score nationwide is 21, about a 1060 on the SAT.

Universal exams cannot, by themselves, close gaps between poor and rich students in college attendance. But in Michigan, it has produced small increases, especially at four-year colleges and particularly among disadvantaged students. The story is similar in Maine, Illinois and Colorado.

Professor Hyman calculates that at a cost of less than $50 per student, a universal testing program is one of the least expensive ways to increase college attendance. Further, if the SAT or ACT replaces the standardized test that states require in public schools, it need not take up any additional instructional time, a key concern of testing opponents.

Many people worry that college admissions tests are biased against low-income and nonwhite students. But disadvantaged students who do not take the tests are out of the running for selective colleges. While we may wish for a better approach, these tests are a gateway to selective schools.

In high-achieving suburban schools where parents are loudly rebelling against standardized tests, nearly all children take the SAT or ACT, as well as test-preparation courses. Giving these tests at no cost during school simply levels the playing field.