Exactly like any other field of knowledge, music (in its learning process) depends largely on the role of the teacher.
Elements such as stimuli, information, tips, technique of the instrument, general musical knowledge, the cultivation of aesthetic criterion, the "opening" of the ("thirsty") spirit and its redirection towards "wealthier sources", the love and devotion to music, the call to the inner quest for self-knowledge and liberation of the self and the inspiration that the student seeks, are highly necessary for music guidance, which needs to be provided profusely and selflessly by the music "teacher".

In jazz music all the above become even more necessary and urgent, since the personality and spiritual growth of each musician are catalytic elements for the value of his musical entity and creation.

Having thus identified the main features that the path to the music knowledge should contain and having assessed the enormous contribution and importance of the teacher-mentor, let's look at how can one find the "appropriate teacher."

As we've said before... "In the beginning there was sound" (read the related article on sound), therefore the first thing we perceive (consciously or unconsciously) when we hear a musical instrument, is always its sound.
The dominant element that should lead the student towards the appropriate teacher is obviously the sound of the particular teacher and in the case of jazz singing, it's the sound of his singing voice.

The first and quite infallible criterion is the "identification" of the student with the sound of his/her teacher. Out of pure instinct and without any musical knowledge or developed evaluative criteria, the learner is largely able to perceive the beautiful sound in a voice. Learning to sing properly is a difficult and complex process that relies enormously to imitation... so it is very easy to realize how "vulnerable" the student can be regarding the "information" that his/her ear perceives. Therefore it is crucial that the teacher has an open, clear, free and natural sound, because it's the only way to ensure that the auditory stimulus, that the student will be called to imitate, is technically the most beneficial for his/her own vocal development and maturation.

A second criterion, that the student should keep in mind in his/her search for the right music teacher, is the training and experience of the teacher, that he/she will eventually choose.
It is particularly useful for his/her evolution, to take all knowledge (technical, musical, etc) from a methodical teacher who has the indispensable inventiveness to "transmit" it in the most effective way. And of course,  it is essential for the student to be "inspired" by the teacher-mentor... therefore it is highly necessary that the teacher can actually do (in practice) everything that he/she teaches in theory.
In very general terms... it is not possible to theorize about the groove, the phrasing, improvisation, etc and not be able to improvise after all !

And the third and last criterion, which is directly connected to the previous one, is the presence of the teacher on the stage, in this case, the jazz scene. Especially in jazz music, which is constantly evolving, the teacher should be an active musician, playing this music, studying, continuously evolving, in order to meet the constant demands and challenges, as a teacher and as a performer, too.

The role of the teacher is to guide the student towards the knowledge and skills that will help him/her develop into a complete musical personality with confidence, maturity and openness. To instill honesty, aesthetics and sincerity to the student, in order for him/her to become a musician with self awareness, who appreciates the virtues of other musicians (and his/her own, of course) and enjoys playing music with his/her colleagues.
Above all, what the teacher must impart to the student, is the selfless love for music.