The Eccles' expectancy-value model posits that a cascade of mechanisms explain associations between parents' beliefs and youths' achievement-related behaviors. Specifically, parents' beliefs predict parents' behaviors; in turn, parents' behaviors predict youths' motivational beliefs, and youths' motivational beliefs predict their behaviors. This investigation focused on testing this model with mothers in sports, music, math, and reading over a 12-year period. Data were drawn from mother, youth, and teacher questionnaires collected as part of Childhood and Beyond Study (92% European American; N = 723). Mothers' beliefs in sports, music, and math positively predicted their behaviors in these areas 1 year later, which predicted youths' self-concepts of ability and values (i.e., their motivational beliefs) in these domains 1 year later. Adolescents' motivational beliefs predicted time spent in organized sport activities, playing music, and reading after school measured 4 years later as well as the number of math courses taken in high school. Furthermore, except in reading, mothers' behaviors mediated the relations between mothers' and youths' beliefs, and youths' beliefs mediated the relations between mothers' behaviors and youths' behaviors. Although there were mean-level differences in several indicators based on child gender, in most cases the relations among these indicators did not significantly vary by child gender. This study highlights the processes by which mothers' beliefs during their children's childhood can predict children's activities in adolescence. (Contains 3 tables, 1 figure and 1 footnote.)