The following article contains an answer for the question: What is the name of the group to which George Martin functioned as an informal music teacher? , can you please find it? 

George Martin's close involvement in his role as producer made him one of the leading candidates for the informal title of the "fifth Beatle". He applied his classical musical training in various ways, and functioned as "an informal music teacher" to the progressing songwriters, according to Gould. Martin suggested to a sceptical McCartney that the arrangement of "Yesterday" should feature a string quartet accompaniment, thereby introducing the Beatles to a "hitherto unsuspected world of classical instrumental colour", in MacDonald's description. Their creative development was also facilitated by Martin's willingness to experiment in response to their suggestions, such as adding "something baroque" to a particular recording. In addition to scoring orchestral arrangements for recordings, Martin often performed on them, playing instruments including piano, organ and brass.Collaborating with Lennon and McCartney required Martin to adapt to their different approaches to songwriting and recording. MacDonald comments, "while [he] worked more naturally with the conventionally articulate McCartney, the challenge of catering to Lennon's intuitive approach generally spurred him to his more original arrangements, of which 'Being for the Benefit of Mr. Kite!' is an outstanding example." Martin said of the two composers' distinct songwriting styles and his own stabilising influence:
Compared with Paul's songs, all of which seemed to keep in some sort of touch with reality, John's had a psychedelic, almost mystical quality ... John's imagery is one of the best things about his work – 'tangerine trees', 'marmalade skies', 'cellophane flowers' ... I always saw him as an aural Salvador Dalí, rather than some drug-ridden record artist. On the other hand, I would be stupid to pretend that drugs didn't figure quite heavily in the Beatles' lives at that time ... they knew that I, in my schoolmasterly role, didn't approve ... Not only was I not into it myself, I couldn't see the need for it; and there's no doubt that, if I too had...

Beatles