Developmental scientists have argued that the implementation of longitudinal methods is necessary for obtaining an accurate picture of the nature and sources of developmental change (Magnusson Morrison & Ornstein, 1996). Developmentalists studying cognition have been relatively slow to embrace longitudinal research, and thus, few exemplar studies have tracked individual children's cognitive performance over time and even fewer have examined contexts that are associated with this growth. In this article, we first outline some of the benefits of implementing longitudinal designs. Using illustrations from existing studies of children's basic cognitive development and of their school-based academic performance, we discuss when it may be appropriate to employ longitudinal (vs. other) methods. We then outline methods for integrating longitudinal data into one's research portfolio and contrast the leveraging of existing longitudinal data sets with the launching of new longitudinal studies to address specific questions concerning cognitive development. Finally, for those who are interested in conducting longitudinal investigations of their own, we provide practical on-the-ground guidelines for designing and carrying out such studies of cognitive development.