Dunn’s most inspired teaching was probably achieved at the Grand Central School of Art, which was established by the Grand Central Art Galleries and located on the top floor of Grand Central Terminal in New York City. His comments were captured by a student during a five-hour class session and were published in 1934 in a slim volume titled "An Evening in the Classroom". Dunn was a demanding teacher and at times a harsh critic. He believed in preparing his students for the harsh realities and intense competition of the commercial world. Talent was not enough. As he once said, “If you ever amount to anything at all, it will be because you are true to that deep desire or ideal which made you seek artistic expression in pictures.” Other students included Dean Cornwell, James E. Allen, Harry Beckhoff, John Clymer, Mac Conner, Dan Content, Mario Cooper, Wilmot Emerton Heitland, Walt S. Louderback, Henry Clarence Pitz, Arthur Sarnoff, Mead Schaeffer, Harold Von Schmidt, Frank Street, and Saul Tepper.