This article examines the use of shadow education by students of compulsory secondary education in Spain over the period 2000-2010. The study identifies the proportion of the student population that uses this type of education and examines how the use of shadow education has evolved during this period. Data was drawn from the student questionnaire in the PISA report, which gathered information on extra lessons in the four studies conducted between 2000 and 2009. The study also contrasted the data on the use of extra classes with the socioeconomic profile of students and other indicators of social inequality.