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 7th-grade adolescents (M-age = 12.5 years, N = 194, 52% female) was measured longitudinally on use of tobacco, alcohol, and marijuana. Mothers, fathers, and adolescents all reported on consistent discipline and monitoring of adolescents. Both consistent discipline and monitoring 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 United States, 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.