Kaplan's interest in Mahler's Symphony No 2 dated back to 1965. In 1981, he began tutelage in conducting with Charles Zachary Bornstein. He rented Avery Fisher Hall in New York for his public conducting debut in 1982, leading the American Symphony and the Westminster Symphonic Choir. Originally, the orchestra had requested that no reviews be published, but Leighton Kerner of "The Village Voice" breached this requested embargo with a positive review of this performance. Subsequently, Kaplan conducted Mahler's Symphony No 2 in over 100 live performances over the remainder of his life. He established the Kaplan Foundation, dedicated to scholarship and the promotion of the music of Gustav Mahler. After personal research, he twice recorded Mahler's Second Symphony: with the London Symphony Orchestra in 1987, and with the Vienna Philharmonic in 2002. Mahler's Second Symphony was the only complete work he conducted in public, although he did separately record the Adagietto from Mahler's Symphony No. 5 in a studio recording.