Measuring the distance between countries and the goal of equality of opportunity in education has been the focus of recent contributions in the economic literature, which have concentrated either on intergroup gaps in access to a given level of studies or on intergroup gaps in educational achievement. We argue that both aspects are important and interrelated and, as a consequence, should be measured simultaneously and combined in a composite index of equality of opportunity in education. Employing recent PISA data for a selected set of countries, rank reversals are observed with respect to orderings based upon a single dimension. The index can be generalized to include further dimensions, such as average scores or dissimilarity in access.