Much has been written about the need for high-quality science, technology, engineering, and mathematics (STEM) teachers and their role in U.S. educational reform. In this article we provide evidence that beginning science and mathematics teachers need a blend of three mutually reinforcing learning opportunities for growth and sustainability: content-rich professional community, pedagogical inquiry, and leadership from the classroom. We describe how a five-year teaching fellowship program supported these opportunities and argue that these opportunities build professional capital, which offers more powerful leverage for STEM teacher quality and retention than focusing on individual teacher development alone.