As a primary goal, educators often strive to maximize the amount of information pupils remember. In the lab, psychologists have found efficient memory strategies for retaining school-related materials. One such strategy is the spacing effect, a memory advantage that occurs when learning is distributed across time instead of crammed into a single study session. Spaced learning is not often explicitly utilized in actual classrooms, perhaps due to a paucity of research in applied settings and with school-aged children. The current study examined the spacing effect in real-world fifth-grade classrooms. We taught 39 children unfamiliar English words using both massed and spaced learning. Five weeks later, we tested vocabulary recall. One-week spacing produced superior long-term retention compared to massed learning. This finding demonstrates that the spacing effect can be generalized to vocabulary learning in applied settings and middle-school-aged children. Copyright © 2010 John Wiley & Sons, Ltd.