Exemplary science, technology, engineering, and mathematics (STEM) learning has been challenging to identify and replicate. Drawing on STEM literature by school level and an analytic framework for collective leadership, this multiple-case study of five exemplary STEM schools compares conditions, barriers, and variations by school level. Over 2 years, we used surveys, focus groups, interviews, and site visits to collect data on all schools (two elementary, one middle, and two high). The five schools were characterized by "STEM cultures" that demonstrated an engineering mindset exemplified by design thinking, prototyping, and strong orientations toward improvement. The two elementary schools in the study had particularly strong working relationships and shared influence among teachers that allowed for the spread of expertise and collective willingness to take risks. Strong teacher leadership, supported by administration, was particularly influential on STEM teaching that included improved social-emotional learning around collaboration and empathy.