koechlin began assisting fauré in teaching fugue and counterpoint while he was still a student in the 1890s, but though he taught privately and was an external examiner for the paris conservatoire throughout his career, he never occupied a permanent salaried teaching position. composers who studied with him included germaine tailleferre, roger désormière, francis poulenc and henri sauguet. cole porter studied orchestration with him in 1923–24. darius milhaud, though never a pupil, became a close friend and considered he learned more from koechlin than any other pedagogue. koechlin wrote three compendious textbooks: one on harmony (3 vols, 1923–26), one on music theory (1932–34) and a huge treatise on the subject of orchestration (4 vols, 1935–43) which is a classic treatment of the subject. koechlin’s treatise uses examples from the orchestral repertoire of the late 19th and early 20th centuries, in particular including examples form french composers, such as saint-saens, debussy, chabrier, bizet, fauré, ravel, and koechlin himself.