Field Elementary School in Littleton, Colorado, had previously seen success with its pullout model of instruction for English language learners. However, as the English language learner (ELL) population increased to 42 percent, the school's performance on state assessments dropped, and it was clear that something different was needed. School leaders decided to implement co-teaching to enable ELLs to receive classroom instruction all day. Under this new plan, classroom teachers would be paired with an English language development teacher to provide language and content instruction simultaneously. The school put together a professional learning plan in which partners would together learn how co-teaching relationships would work. As the model was implemented, the school learned that teachers needed additional support, so leaders worked with the co-teachers to better define the teacher's roles and prepare lesson plans that made use of both teachers' expertise. After just one year of using this model, Field achieved Colorado's highest possible rating for student growth, and the model has expanded to the whole district.