The present paper introduces a new indicator of educational inequality, the grade distribution ratio (GDR), focusing on levels of grade repetition and drop out rates in primary and secondary education. The indicator is specifically suitable to evaluate the distributive implications of expanding educational systems in developing countries. A comparative analysis of grade enrollment distributions across 92 developing countries from 1960 to 2005 reveals that the decline in educational inequality has been substantial and wide spread since 1960, but that progress has slowed down in the last two decades. Latin American countries were characterized by very large initial levels of educational inequality, but contrary to other developing regions continued to equalize their grade enrollment distribution in the last two decades.