exception of a quotation in the social statistics. It generally employs the expression of "écoles supérieures" to indicate higher educational institutions that are not universities. The Conférence des grandes écoles (CGE) (Grandes Écoles Conference) is a non-profit organization. It uses a broad definition of grande école, which is not restricted to the school's selectivity or the prestige of the diploma awarded. The members of CGE have not made an official or "accepted" list of grandes écoles. For example, some engineering school members of the CGE cannot award state-recognized engineering degrees. Admission to grandes écoles Admission to grandes écoles is different from that to French universities. To be admitted into most French grandes écoles, most students study in a two-year preparatory program in one of the CPGEs (see below) before taking a set of competitive national exams. Different exams are required by groups (called "banques") of different schools. The national exams are sets of written tests, given over the course of several weeks, that challenge the student on the intensive studies of the previous two years. During the summer, those students who succeed in the written exams then take a further set of exams, usually one-hour oral exams, during which they are given a problem to solve. After 20 minutes of preparation, the candidate presents the solution to a professor, who challenges the candidate on the answer and the assumptions being made. Afterwards, candidates receive a final national ranking, which determines admission to their grande écoles of choice. Preparatory classes for grandes écoles (CPGE) Classes préparatoires aux Grandes Écoles (CPGE), or prépas (preparatory classes for grandes écoles), are two-year classes, in either sciences, literature, or economics. These are the traditional way in which most students prepare to pass the competitive recruitment examination of the main grandes écoles. Most are held in state lycées (high schools); a few are private. Admission is competitive and based on the students' lycée grades. Preparatory classes with the highest success rates in the entrance examinations of the top grandes écoles are highly selective. Students who are not admitted to the grande école of their choice often repeat the second year of preparatory classes and attempt the exam again the following year. There are five categories of prépas: Scientifiques: These prepare for the engineering schools and teach mathematics, physics, chemistry, and technology. They are broken down in sub-categories according to the emphasis of their dominant subject: they