e. b and c above.

The students tanked all three pretests, performing no better than if they had guessed at random. Bjork and Soderstrom had expected as much. But the class received prompt feedback, attending the relevant lecture shortly after they took each of the three pretests. Those lectures in effect supplied them with correct answers to questions that had just been posed on the pretest. In previous experiments, such immediacy seemed to be a critical component: Pretests led to the most improvement when students received the correct answers reasonably soon after their guessing.

In order to gauge the effect of the testing, Bjork and Soderstrom gave a cumulative exam at the end of the 10-week course. It was the same format as the others: multiple-choice questions, each with five possible answers. The result? Bjork’s Psych 100B class scored about 10 percent higher on the related questions than on the unrelated ones. It’s far from a magic memory pill — but 10 percent, as we all know, can often translate to a letter grade. “On the basis of this significant difference,” Bjork said, “giving students a pretest on topics to be covered in a lecture improves their ability to answer related questions about those topics on a later final exam.” Even when students bomb, she said, pretests provide them an opportunity to see what vocabulary will be used in the coming lectures, what kinds of questions will be posed and which distinctions between concepts will be crucial.

Bjork’s experiment suggests that pretesting serves to prime the brain, predisposing it to absorb new information. Scientists have several theories as to how this happens. One is fairly obvious: Students get a glimpse from a pretest of the teacher’s hand, of what they’ll be up against. That’s in the interest of not just students but of teachers, too. You can teach facts and concepts all you want, but what’s most important in the end is how students think about that material: How they incorporate all those definitions into a working narrative about a topic that gives them confidence in judging what’s important and what’s less so. These are not easy things to communicate, even for the best teachers. You can’t download such critical thinking quickly, hard as you might try. But you can easily give a test with questions that themselves force that kind of hierarchical thinking. “Taking a practice test and getting wrong answers seems to improve subsequent study, because the test adjusts our thinking in some way to the kind of material we need to know,” Bjork said.

A second possibility has to do with the concept of fluency. Wrong guesses expose our fluency illusions, our false impression that we “know” the capital of Eritrea because we just saw it or once studied it. A test, if multiple-choice, forces us to select the correct answer from a number of possibilities that also look plausible. “Let’s say you’re pretty sure that Australia’s capital is Canberra,” Robert A. Bjork, Elizabeth Ligon Bjork’s husband and a leading learning scientist, said. “O.K., that seems easy enough. But when the exam question appears, you see all sorts of other possibilities — Sydney, Melbourne, Adelaide — and suddenly you’re not so sure. If you’re studying just the correct answer, you don’t appreciate all the other possible answers that could come to mind or appear on the test.” Pretesting operates as a sort of fluency vaccine.

Biologically, too, there may be something deeper at work. To review, memory builds on itself in ways we don’t usually notice. Retrieval — i.e. remembering — is a different mental act than straight studying; the brain is digging out a fact, together with a network of associations, which alters and enriches how that network is subsequently re-stored. But guessing is distinct from both study and retrieval. It too will reshape our mental networks by embedding unfamiliar concepts (the lend-lease program, the confirmation bias, the superego) into questions we at least partly comprehend (“Name one psychological phenomenon that skews our evaluation of evidence”). Even if the question is not entirely clear and its solution unknown, a guess will in itself begin to link the questions to possible answers. And those networks light up like Christmas lights when we hear the concepts again.

And here is where pretesting shows its likely limitations: A prefinal for an intro class in Arabic or Chinese could be a wash, because the notations and characters are entirely alien. There’s no scaffolding of familiar language to work with — no existing network in which to situate the new symbols — before we make a guess. We are truly lost, with no recognizable landmark. The research thus far suggests that prefinals will be much more useful in humanities courses and social-science disciplines in which unfamiliar concepts are at least embedded in language we can parse.

The word “testing” is still loaded, of course, in ways that have nothing to do with learning science. Educators and experts have debated the value of standardized testing for decades, and reforms like the No Child Left Behind law, which increased the use of such exams, have only inflamed the argument. Many teachers complain that a focus on testing limits their ability to fully explore subjects with their students. Others attack tests as woefully incomplete measures of learning, blind to all varieties of creative thinking.

But the emerging study of pretesting flips that logic on its head. “Teaching to the test” becomes “learning to understand the pretest,” whichever one the teacher chooses to devise. The test, that is, becomes an introduction to what students should learn, rather than a final judgment on what they did not.