Here's a pop quiz: What foods are best to eat before a high-stakes test? When is the best time to review the toughest material? A growing body of research on the best study techniques offers some answers.

Chiefly, testing yourself repeatedly before an exam teaches the brain to retrieve and apply knowledge from memory. The method is more effective than re-reading a textbook, says Jeffrey Karpicke, an assistant professor of psychological sciences at Purdue University. If you are facing a test on the digestive system, he says, practice explaining how it works from start to finish, rather than studying a list of its parts.

In his junior year of high school in Cary, N.C., Keenan Harrell bought test-prep books and subjected himself to a 'relentless and repetitive' series of nearly 30 practice SAT college-entrance exams. 'I just took it over and over again, until it became almost aggravating,' he says.

Practice paid off. Mr. Harrell, now 19, was accepted at University of North Carolina-Chapel Hill, a college he's dreamed of attending since the third grade. He scored 1800 (out of 2400) on the SAT, up 50% from 1200 on the PSAT, a preliminary test during his sophomore year.

Taking pretests 'felt like hard work,' Mr. Harrell says, but seeing steady increases in his scores boosted his confidence. Practice tests also help with test-taking skills, such as pacing, says Paul Weeks, vice president of educational services for the ACT, which creates and administers college-entrance exams.

Sleep also plays a role in test performance, but in two unexpected ways. Review the toughest material right before going to bed the night before the test. That approach makes it easier to recall the material later, says Dan Taylor, director of a sleep-and-health-research lab at the University of North Texas in Denton. And don't wake up earlier than usual to study; this could interfere with the rapid-eye-movement sleep that aids memory, he says.

A common study habit