Students around the world are going to school but are not learning - an emerging gap in human capital formation. To understand this gap, this paper introduces a new data set measuring learning in 164 countries and territories. The data cover 98 percent of the world's population from 2000 to 2017. The data set will be publicly available and updated annually by the World Bank. The paper presents several stylized facts in a first application of the data: (a) although enrollment has increased worldwide, learning has stagnated; (b) girls outperform boys on learning - a positive gender gap - in contrast to a negative gender gap observed for schooling; (c) learning is associated with growth on a global scale; (d) associations with growth are heterogenous; and (e) human capital accounts for up to a third of cross-country income differences - a middle ground in the recent development accounting literature. These stylized facts demonstrate the potential of the data to reveal new insights into the relationship between human capital and economic development.