Among U.S. Mexican adolescents living in established immigrant communities, high familism values are positively associated with compliant, emotional, and dire prosocial behaviors via sociocognitive and cultural psychological mechanisms. Less is known about the behavioral mechanisms that may explain these associations, or about prosocial behaviors among U.S. Latinxs residing in emerging immigrant destinations. We examined the cross-sectional, intervening variable associations among familism values, family assistance behaviors, and culturally salient prosocial behaviors among 547 U.S. Latinx adolescents residing in an emerging immigrant destination (M age = 12.8 years; 55.4% girls). Familism values and family assistance behaviors promoted emotional and dire prosocial behaviors for boys and girls, and promoted compliant prosocial behaviors for boys only. Familism also had direct associations with all three prosocial behaviors for boys and girls. Family assistance behaviors may be a mechanism via which adolescents develop compliant, emotional, and dire prosocial behaviors.