Despite the fact that most boys and girls are in classrooms together, there is considerable variation in the degree to which their classrooms reflect gender integration (GI). In some classrooms, boys' and girls' relationships with each other are generally positive and harmonious. However, in other classes, students tend to only work with classmates of the same gender (i.e., gender segregation, GS), and cross-gender interactions seldom occur or, when they do, they may not be positive. As such, the coeducational context of schools provides no assurance that boys and girls work effectively together to learn, solve academic problems, and support one another in their academic efforts. The purpose of this perspective paper is to call attention to the importance of studying and understanding the role of GI in contemporary U.S. coeducational classrooms. Some of the costs associated with the failure to consider GI also are identified, as are implications for future research and educational practice.