Low-income students often lose the academic gains they made during the school year during class-free summer vacation, a phenomenon called the “summer slide.” The solution? Free books. Seven states are participating in an experimental program—designed to help close the achievement gap between middle-class and low-income students—that will fill kids’ arms with free paperbacks, which research indicates might be as effective as summer school, for a much lower price. Summer slide accounts for as much as 80 percent of the achievement gap; middle class kids have more books at home, which gives them an advantage by the time classes resume in the fall. In a recent study, students who received 12 free books on the last day of school for three years straight had “significantly higher” reading scores and a smaller summer slide.