His biggest breakthrough till then came in 1955, when his Symphony No. 2, Mysterious Mountain, was premiered by Leopold Stokowski in his debut with the Houston Symphony, although the idea that Mysterious Mountain was commissioned for that orchestra is a Common misconception. That same year, MGM Records released recordings of a number of his works. Between 1956 and 1958, at the urging of Howard Hanson, an admirer of his music, he taught summer sessions at the Eastman School of Music long presided over by Hanson.