The classes préparatoires aux grandes écoles (CPGE) (English: Higher School Preparatory Classes), commonly called classes prépas or prépas, are part of the French post-secondary education system. They consist of two very intensive years (extendable to three or exceptionally four years) which act as a preparatory course (or cram school) with the main goal of training undergraduate students for enrollment in one of the grandes écoles. The workload is one of the highest in the world (between 35 and 45 contact hours a week, plus usually between 4 and 6 hours of written exams, plus between 2 and 4 hours of oral exams a week and homework filling all the remaining free time).
The students from CPGE have to take national competitive exams to be allowed to enroll in one of the Grandes Écoles. These Grandes Écoles are higher education establishments (graduate schools) delivering master's degrees and/or doctorates. They include science and engineering schools, business schools, the four veterinary colleges and the four écoles normales supérieures but do not include medical institutes or architecture institutes. Their competitive entrance exams make having attended one of the grandes écoles being often regarded as a status symbol as they have traditionally produced most of France's scientists, executives and intellectuals (École Polytechnique, écoles normales supérieures, ParisTech Schools, CentraleSupélec schools...).
Hence, there are three kinds of different prépas: scientific, economic and literary CPGE. Each of them prepare to pass the competitive exams of those grandes écoles.