Final answer:
George Gershwin left high school to become a pianist in a publisher's salesroom. This was the beginning of his career in music, where he became a famous American composer.
Step-by-step explanation:
Gershwin left high school at the age of fifteen to become a pianist demonstrating new songs in a publisher's salesroom. This formative experience in his youth set Gershwin on a path to becoming one of the most renowned American composers, known for bridging the gap between classical music and jazz influences. Unlike the example of Marc Chagall, who although facing restrictions due to being Jewish, pursued art by copying illustrations and later attending art schools, Gershwin found his way into music directly through practical engagement in a commercial setting. Gershwin's early departure from traditional education was a stepping stone in his musical career.