Teachers, like the students they serve, never stop learning. In-service teacher professional development (PD) gives educators opportunities over the course of the year to learn more about pedagogy and improve their own instruction methods to boost students' academic and social and emotional outcomes. On average, teachers participate in ten days of inservice PD during the school year. In this research, the authors evaluate the Chicago Collaborative, a teacher PD program that is aligned to Common Core State Standards (CCSS) and implemented by Leading Educators. The research took place during the 2018-2019 and 2019-2020 school years in 40 schools across three school districts in the Chicago area. The authors sought answers to two interrelated questions: (1) How is the Chicago Collaborative PD program implemented?; and (2) Did the Chicago Collaborative PD program impact student achievement? The research found that the Leading Educators Chicago Collaborative was implemented overall as intended and had a statistically significant positive effect on student achievement.