Purpose: For bilingual children with developmental language disorder (DLD), language treatment response is the degree to which an individual child progresses in both of their languages. Understanding what predicts language treatment response for an individual child can help clinicians plan treatment more effectively. Method: This study is a retrospective analysis of data from the study of Ebert et al. (2014). Participants included 32 school-age Spanish-English bilingual children with DLD who completed an intensive language treatment program. Gains in Spanish and English were measured using raw test scores in each language. Predictors of language gains include language, cognitive, and demographic variables. To examine which predictors were significant, we calculated partial correlations between the potential predictors and the posttreatment language test scores, controlling for the effects of pretreatment test scores. Results: In Spanish, several predictors correlated with the outcome measures. After controlling for pretreatment scores, English grammaticality, female sex, processing speed, age, and fluid reasoning were related to Spanish posttreatment scores. In English, correlations with individual predictors were minimal. After controlling for pretreatment scores, only one variable was associated with one English posttreatment score: English grammaticality. Conclusions: The original study reported limited gains in Spanish compared to robust gains in English. Treatment response in Spanish is more variable given the lack of environmental support for Spanish in the United States. As a result, individual factors (including nonverbal cognition, pretreatment language levels, and demographic variables) influence treatment gains in Spanish. In contrast, strong environmental support for English supports a more consistent treatment response, with a smaller role for individual factors.