From 1820 to 1829
From 1820 to 1829, in order to make it clear that the school was providing higher education, its students wore a uniform similar to that of the engineering schools of that era, with a blue frock coat, sword and bicorne. Only a clear band on the pants made the difference with the Polytechnicians’ and Centraliens’ uniforms.
France just emerged from an almost uninterrupted 20-year period of war and one of the first directors of the school was himself a former Napoleon soldier. Order was kept in the military way. All internal movements of the school (recess, beginning and end of classes...) were announced to the sound of the drum, and the boarders’ wake-up call was at five thirty in the Summer (six thirty in Winter).
In 1829, the death of director Henri Monnier des Taillades, who played an essential role in the school's life, caused a degree of uncertainty, and discipline slackened. Just ahead of the Summer holidays, a student outing degenerated into heckling at the Fort de Vincennes, and, as a punitive measure, the Minister of Public Instruction decided that from then on, the students would wear civilian clothing.
Nowadays, whether students wear jeans or suits - nobody ever complains about it.