At first Hindemith was enthusiastic about his violin teacher. In a letter of 27 December 1913 he reported: «His praise makes my work easier and his kindness and friendliness mean more to me that if he were to give me money (which means a lot to a musician)... In the manner of his playing, too, I prefer him to most of the well-known virtuosi.»
This initial enthusiasm for his teacher gradually cooled, however. After Hindemith had been a member of the Rebner Quartet for seven years, he left the ensemble in 1921 after a quarrel with Rebner.
The relationship with Fritz Bassermann, from whom Hindemith received instruction in conducting, was considerably less complicated than that with Adolph Rebner. Bassermann's versatility, his earthy humour and his more practical conception of music were more congenial to Hindemith. (P. Cahn)
Hindemith received his first instruction in composition from Arnold Mendelssohn, a man with a fine, all-round education. In a letter of 27/28 December 1913 he reported that Mendelssohn had taught him «to exploit and utilise what I had learnt before.» Mendelssohn insisted on a technical and formal logic in composition that Hindemith felt to be a burden at first. In his list of works he made the following note about the (meanwhile lost) Theme with Variations in E-flat Major: «Worked at it endlessly. I could hardly please the old man [Mendelssohn].» Hindemith later dedicated his Kammermusik No. 5, Op. 36 No. 4 to Mendelssohn in 1927.
When Mendelssohn fell ill in October 1913, Bernhard Sekles took over the remaining training. Hindemith was primarily grateful to him for compositional craftsmanship. Under the supervision of Sekles, Hindemith developed his first independent compositions. Hans Rosbaud, a fellow student of Hindemith, remembered: «Sekles was a humorous spirit. He knew how to outline problems clearly and sharply, with few words. So we sat full of enthusiasm in Sekles's counterpoint class...» Hindemith was sceptical of Sekles at first. But it was Bernhard Sekles who recognised and encouraged Hindemith's compositional talent, and he was also the one who created the relationship between Paul Hindemith and Schott Music Publishers.