This paper describes the evolution of the coverage of secondary education in Colombia. We combine impact evaluation techniques and cost-benefit analysis to compare the quality of public and private secondary education. We document that the increase of the public enrollment is crowding-out the private supply, and we show a considerable variation in the standardized test (Saber 11) results within public schools. In some cities and socioeconomic strata, some students attending public schools of lower quality than the available private schools, and others are atttending to private in places with better available public supply. Finally, our results show that if the government encourages families to transit from public school to private (through partial scholarships award), it could generate social profits. Similar profits could be generated if the government regulates the low quality of private education in some cities and socioeconomic strata with public schools of better quality.