Maintaining focused attention in the classroom is considered an important factor for successful learning. Loss of instructional time due to off-task behavior is recognized as a significant challenge by both researchers and practitioners. However, there has been little research into the factors contributing to off-task behavior. This paper reports results from the first large-scale study investigating how elementary school children allocate their attention in classroom environments and how patterns of attention allocation change as a function of gender, grade level, and instructional format. The findings indicate that instructional format is related to off-task behavior in elementary school students. These findings can begin to form a foundation for development of research-based guidelines for instructional design aimed to optimize focused attention in classroom settings.