The large majority of the students are admitted after two to three years of classes préparatoires, known as "mathematics superior" and "mathematics special", which are an undergraduate courses with almost exclusive emphasis on math and physics. These undergraduate students must then take a nationwide competitive entrance examination (Concours Centrale-Supélec) to enter a Centrale Graduate School, including Ecole centrale de Lyon. Ecole centrale de Lyon recruits among the top 6% of the students in "classes preparatoires", who represent themselves 7% of higher education students, which makes it a selective and prestigious institution.