His early compositions are typically triadic, often with widely spaced harmonies, giving them a distinctly American tone, but some of his works are consciously French in style.

He was a longtime member of the Juilliard School faculty, his notable students including Alan Belkin, Robert Black, Kenneth Fuchs, Albert Glinsky, Daron Hagen, Adolphus Hailstork, Anthony Iannaccone, Philip Lasser, Lowell Liebermann, Alasdair MacLean, Charles Strouse, Francis Thorne, Kendall Durelle Briggs and Eric Whitacre.

[5][6] According to an obituary in The Guardian however, "He enjoyed enormous success in the 1940s and early '50s with champions that included Koussevitzky, Bernstein, Munch, Ormandy and Mitropoulos but, in the 1960s and '70s, the serial and modernist schools pushed him into the shadows.

"[7] The New York Times similarly referred to Diamond as "a major American composer whose early brilliance in the 1940s was eclipsed by the dominance of atonal music...

He was part of what some considered a forgotten generation of great American symphonists, including Howard Hanson, Roy Harris, William Schuman, Walter Piston and Peter Mennin.