We evaluated whether differences in treatment effectiveness or preference between languages emerged across Spanish and English during functional communication training (FCT) for young children with developmental disabilities exposed to Spanish and English in the home environment. Participants were 2 young children with developmental disabilities who displayed destructive behavior maintained by social contingencies and whose families spoke Spanish and English at home. All procedures were conducted in the participants’ homes by their mothers with coaching from the investigator. The effectiveness of FCT was evaluated within a reversal design across baseline, FCT, and extinction conditions. A multielement design across language type (Spanish and English) was embedded within the reversal design during the extinction and FCT conditions to evaluate differences in treatment effectiveness across type of language. Finally, during all FCT sessions, a concurrent schedules design was used to evaluate participant preference for type of language. Results suggested that FCT was effective in reducing destructive behavior, increasing manding, and/or increasing task completion for these 2 participants across Spanish and English treatment conditions. Preference for the type of language did not emerge for either participant during FCT. Results are discussed in terms of the merits of systematically evaluating language variables when working with culturally and linguistically diverse families and children.