During the 1940s and for many years, Marsh became an important teacher at the Art Students League of New York, which ran a summer camp where Marsh's students included Roy Lichtenstein. Lichtenstein was influenced by Marsh's subject matter in his work. Also in the '40s, Marsh began making drawings for magazines such as Esquire, Fortune, and Life. A degree of mannerism is apparent in his later paintings, in which wraithlike figures "float in a watery netherworld" in a deeper pictorial space than that of his compositions of the 1930s.