For the first time in the history of global education goals, the United Nations Sustainable Development Target 4c specified the increase of qualified teachers as a means to achieve important educational outcomes. Target 4c also identified international cooperation as an important lever to increase the supply of qualified teachers in low-income countries. But what is the evidence that international cooperation can be an effective strategy to increase the supply of qualified teachers in such contexts? We explore this question by examining the educational work of the United States Peace Corps, which has supported teacher quality improvement in over 100 countries. We examine the Peace Corps’ philosophy and approach to educational improvement, the Peace Corps’ efforts to improve teacher quality in low income countries, and evidence of the impact of the Peace Corps’ work on the supply of qualified teachers in the countries where it works. Finally, we discuss important implications and lessons learned from the Peace Corps experience to strengthen the positive impact of international cooperation on teacher quality improvement in developing contexts.