Kay joined the faculty of the Herbert H. Lehman College of the City University of New York in 1968. His title was Professor of Music, and he taught music theory and composition on a full-time basis. In 1965, he had left BMI to take a visiting professorship at Boston University, and from 1966 to 1967, he was Visiting Professor at the University of California at Los Angeles.
In an interview published in the New York Post of June 3, 1968, Kay said that in regard to the many changes that were and are taking place in the music field, he felt that "teaching is right in the thick of it, and the young people are very vitally concerned and interested." He said also that he was happy that he had waited to start teaching later than is the general rule, a time after he had become secure in his own work as a composer. But even while teaching full time, he made time to continue to compose, to conduct, to serve as adjudicator and consultant, to guest lecture, and to participate on composer panels and forums.