Background: Evidence on the treatment effectiveness for bilingual children with primary language impairment (PLI) is needed to advance both theory and clinical practice. Of key interest is whether treatment effects are maintained following the completion of short-term intense treatments. Aims: To investigate change in select language and cognitive skills in Spanish–English bilingual children with PLI 3 months after children have completed one of three experimental treatment conditions. There are two main study aims. First, to determine if skills in Spanish, English and cognitive processing decline, improve or are maintained after treatment has been completed. Second, to determine if differential rates of change are a function of the type of treatment children received. Methods & Procedures: Participants were 48 children, aged 5:6–11:3, who spoke Spanish and English and were diagnosed with moderate to severe PLI. Participants received 6 weeks of treatment focused on English only (EO), bilingual skills in Spanish and English (BI) or nonlinguistic cognitive processing (NCP). Treatment effects reported in a previous study were determined by comparing pre- and post-treatment performance on a variety of language and cognitive measures. Here we re-administered each measure 3 months after completion of the experimental treatments. Hierarchical linear models were calculated for each measure using pre-, post- and follow-up testing scores to estimate change trajectories and compare outcomes between treatment conditions. Outcomes & Results: Participants in all three treatment conditions either maintained skills or showed improvement even after treatment was discontinued for 3 months. Main findings included (1) comparable, positive rates of change on all English language outcomes for EO and BI conditions; (2) maintenance of Spanish language skills, and (3) modest improvements in NCP following the discontinuation of treatment. Conclusions & Implications: This study is the first to examine longer-term treatment effects for bilingual school-age children with PLI. Differences in rates of change between languages and between treatment conditions are discussed in terms of social and cognitive processes that impact children's language systems. The main findings have at least two implications for clinical practice: (1) therapy that emphasizes focused practice in language and cognitive processing skills may promote gains in children's language learning abilities; and (2) bilingual treatment does not detract from outcomes in English, the language of the majority community for study participants.