In 2015 WakeEd Partnership and Wake County Public School System (WCPSS), North Carolina's largest school system, designed an engaging, results-oriented professional development opportunity for elementary and secondary educators -- SummerSTEM. SummerSTEM is a hands-on professional development experience that addresses the needs of educators -- adult learners -- and brings real-world lessons to the classroom. As part of SummerSTEM, teachers receive seven days of professional development (five in the summer and two in the fall) in project-based learning (PBL) following the Buck Institute for Education Gold Standard model. Additionally, they are immersed in STEM businesses and industries to experience work processes and workforce development needs. Teachers, who participate as teams of two, remain focused on integrating the components of PBL with lessons learned from their immersion, as they create PBL units and transform their classroom culture. SummerSTEM culminates in STEMposium, a public event in which teachers and their students share their PBL outcomes. To evaluate SummerSTEM, EvalWorks, a local firm with experience evaluating national/federal, state, and local STEM initiatives conducted surveys, focus groups, and teacher and student interviews to understand impacts. Many participants indicated that they saw themselves increasingly as teacher leaders, which led them to take on new responsibilities and roles, and positively affected not only their view of teaching, but also, for over half of the participants, their decision to remain teaching. The PBL units benefitted students by increasing their opportunities to collaborate and lead, and, as a result, encouraging them to assume greater ownership of their learning. Taken together, findings are that SummerSTEM is a model for effective teacher professional development that positively impacts students by changing teachers' practices and mindsets.