He published a number of instructional books, including Die Kunst des Violin-Spiels (The Art of Violin Playing, 1923) in which he advocated for the violinist as artist rather than merely virtuoso.
Among his pupils were Charles Barkel, Edwin Bélanger, Norbert Brainin, Felix Galimir, Bronislaw Gimpel, Ivry Gitlis, Szymon Goldberg, Ida Haendel, Zvi (Heinrich) Haftel, Josef Hassid, Adolf Leschinski, Alma Moodie, Ginette Neveu, Yfrah Neaman, Ricardo Odnoposoff, Eric Rosenblith, Max Rostal, Henryk Szeryng, Henri Temianka, Roman Totenberg and Josef Wolfsthal, all of whom achieved considerable fame as both performers and pedagogues.
He said his favorite pupil was the Australian Alma Moodie, who achieved great fame in the 1920s and 1930s but made no recordings and is little known today.
One of Flesch's few recordings is a highly distinguished interpretation of Bach's great D minor Double Violin Concerto (Columbia) in which he played second violin to the great Joseph Szigeti, with Walter Goehr conducting an anonymous London string orchestra in the late 1930s.
Because of his Jewish origins,[3] Flesch had to move to London during the 1930s, and was later arrested by the Gestapo in the Netherlands,[4][5][6][7] was released thanks to Furtwängler's intervention,[8] and died in Lucerne, Switzerland, in November 1944.