This chapter presents the achievement gap in Mexico and starts with general data to help readers understand what kind of country Mexico is: it is the 11th most populated country, with the 14th largest GDP (gross domestic product), and ranks 57th on the world human development index (HDI). Then the education in Mexico is analyzed beginning with the distribution of its almost 35 million students in 2010, in preschool (K, with 3 years), primary (1–6), secondary (7–9), middle education (10–12)—all these being compulsory— and superior. To have references of the achievement gap, the evaluation results of two national assessments and the Programme for International Student Assessment (PISA) are discussed, for subject and education level, and then the best and worst federative entities are contrasted. In all of these evaluations, almost half of the students qualify with an insufficient achievement.