He went on to study piano at the Royal College of Music while simultaneously working on the school's opera staff from 1927–1929.
While there he had the opportunity to work closely with Sir Adrian Boult and Ralph Vaughan Williams.
He also frequently worked as a consultant for the opera program at the Toronto Conservatory of Music (TCM), beginning with the school's 1929 production of Vaughan Williams's Hugh the Drover.
[1] While still teaching at the TCM, Mazzoleni was appointed the director of the Opera Division at the University of Toronto (UTOD) in 1952, a post he held until 1966.
Among his notable pupils were musicians Howard Cable, Robert Fleming, James Gayfer, Godfrey Ridout, and Rudy Toth.