This document summarizes a study exploring how educators learn to teach in massive open online courses (MOOCs). The study used a multiple case study approach examining 7 MOOCs taught by 28 educators. It found that educators largely learned through practical experience, with limited formal training or guidance. Their knowledge developed experientially through iterations of courses as they incorporated learner feedback. Collaboration with other educators of varying expertise also supported their learning. The study recommends providing more formal training and guidance to educators on topics like video production and copyright, as well as opportunities for collaboration and apprenticeships to strengthen educators' skills and practices for teaching MOOCs.