Complex sentence: The son of a Philadelphia printer, Kay became a student at Philadelphia's Curtis Institute (1936-1940) where he studied cello and composition under Randall Thompson, in whose classes he was a fellow student of Leonard Bernstein.
Split into simpler sentences: The son of a Philadelphia printer, Kay became a student at Philadelphia's Curtis Institute (1936-1940) where he studied cello and composition under Randall Thompson. In whose classes he was a fellow student of Leonard Bernstein.