This collaborative writing intervention in one CUNY community college examined the effectiveness of mixing English language learners (ELLs) and native English speakers (NES) in advanced-level developmental writing courses. We describe the translingual approach to curriculum and intervention along with promising developmental education practices. We also combine reflections on collaboration and student outcomes with quantitative analysis to allow each of these tools to inform the other, as well as to consider the limits of single-measure analysis of students and programs. The mixing of ELLs and NES fostered a less segregated classroom with student work and language development progressing more than in non-mixed classes. A statistical analysis confirmed these impressions, which suggests a relatively predictable outcome for this intervention. The experiment influenced several changes in departmental and instructor practices.