Born in New York, he moved to Boston in 1920. He was trained in the technique of concert piano by Heinrich Gebhard, Rosina and Joseph Lhevinne and Elizabeth Quaile. In 1941 and 1942 he gave critically acclaimed piano recitals in New York's Town Hall. His playing was recognized by critics and his peers for its depth, maturity, clarity, precision and color. After World War II, Jencks devoted his energies to the composition of piano music, concentrating on sonatas. Through the 1950s and '60s he worked with composers such as Aaron Copland, Henry Cowell, Roger Sessions, Elliott Carter, Walter Piston, Edgard Varese and Arthur Berger.