The development of gender attitudes in 402 youth (201 firstborn and 201 secondborn siblings) in 201 European American families was examined using data collected on seven occasions across 9 years. Pooling across siblings and using multilevel modeling, we examined gender attitude development from ages 7 to 19. Consistent with an ecological perspective, the combined effects of individual (i.e., sex, age, birth order) and contextual (i.e., parents' gender attitudes, sibling sex) characteristics predicted patterns of change. Although most youth declined in traditionality, the attitudes of firstborn boys with brothers and traditional parents became more traditional over time. No one longitudinal pattern captured the development of gender attitudes; trajectories varied as a function of contextual and personal characteristics.