The primary goal of the current study was to test whether parent and adolescent preference for a common language moderates the association between parenting and rank-order change over time in offspring substance use. A sample of Mexican-origin seventh-grade adolescents (mean age = 12.5, N = 194, 52% female) was measured longitudinally on use of tobacco, alcohol, and marijuana. Mother, father, and adolescent all reported on consistent discipline and monitoring of the adolescent. Consistent discipline and monitoring both predicted relative decreases in substance use into early adulthood, but only among parent-offspring dyads who expressed preference for the same language (either English or Spanish). This moderation held after controlling for parent substance use, family structure, having completed schooling in Mexico, years lived in the U.S., family income, and cultural values. An unintended consequence of the immigration process may be the loss of parenting effectiveness that is normally present when parents and adolescents prefer to communicate in a common language.