As reported in the Chronicle of Higher Education, several recent studies confirmed that frequently quizzing students on reading material helps them retain what they have learned.
One study, published in Psychological Science, was based on experiments in which students read passages on scientific topics.

Authors of this study found that the students who were directed to review the material before testing reported greater confidence in their ability to remember the material (and, indeed, they performed better on the retention test given five minutes later). However, on the tests taken days later, "prior testing produced substantially greater retention than studying." To learn more, click here.