School enrollment has universally increased over the last 25 years in low-income countries. Enrolling in school, however, does not assure that children learn. A large share of children in low-income countries complete their primary education lacking even basic reading, writing, and arithmetic skills. Teacher quality is a key determinant of student learning, but not much is known about teacher quality in low-income countries. This paper discusses an ongoing research program intended to help fill this void. The authors use data collected through direct observations, unannounced visits, and tests from primary schools in seven sub-Saharan African countries to answer three questions: How much do teachers teach? What do teachers know? How well do teachers teach?