In 1888, Diémer succeeded Marmontel as professor of piano at the Paris Conservatory. He taught, among others, Robert Casadesus, Alfredo Casella, Marcel Ciampi, Alfred Cortot, José Cubiles, Lazare Lévy, Robert Lortat, Yves Nat, and Édouard Risler. He was also instrumental in promoting the use of historical instruments, giving a series of harpsichord performances as part of the 1889 Universal Exhibition and contributing to the founding of the Société des Instruments Anciens.