MIDDLE SCHOOL students are champion time-wasters. And the personal computer may be the ultimate time-wasting appliance. Put the two together at home, without hovering supervision, and logic suggests that you won’t witness a miraculous educational transformation.

Still, wherever there is a low-income household unboxing the family’s very first personal computer, there is an automatic inclination to think of the machine in its most idealized form, as the Great Equalizer. In developing countries, computers are outfitted with grand educational hopes, like those that animate the One Laptop Per Child initiative, which was examined in this space in April. The same is true of computers that go to poor households in the United States.

Economists are trying to measure a home computer’s educational impact on schoolchildren in low-income households. Taking widely varying routes, they are arriving at similar conclusions: little or no educational benefit is found. Worse, computers seem to have further separated children in low-income households, whose test scores often decline after the machine arrives, from their more privileged counterparts.

Ofer Malamud, an assistant professor of economics at the University of Chicago, is the co-author of a study that investigated educational outcomes after low-income families received vouchers to help them buy computers.