Starting in September 1940, Hindemith's teaching at Yale University was so successful and dedicated that the University tried to win him over for a full professorship already in January 1941. Hindemith accepted the appointment, as he was largely able to assert his conditions at the negotiations which were, at the same time, connected with a fundamentally new organisation of the study of music. With his teaching activity, Hindemith almost formed a school within the school.
He also taught at Tanglewood again in the summer of 1941 and rehearsed a total of 188 works by Perotin (approx. 1200) to Schütz for which he prepared most of the performance material himself. Gertrud Hindemith dedicated herself to social services, studied Romance languages and literature at Yale and passed examinations for a Master's degree.
The Hindemiths, who after Germany's declaration of war on the United States were considered «enemy aliens,» but only had travel restrictions imposed on them, led an anonymous life in New Haven. Their neighbours remembered them as a friendly, helpful, inconspicuous couple and were astonished to find out later that Hindemith was a «famous» composer. They had friendly relations with only a few teaching colleagues at Yale University and avoided contact with European emigrants, but without appearing closed or stand-offish. They resumed their home music-making, cultivated in Bluche, at which friends and students also participated, and travelled only within the New England states during their few holidays in wartime.