I am not sure how relevant this is to the issue you raise, but your question reminds me of the work of colleagues of mine on the mentoring of trainee (and beginning) teachers. Some of their work and ideas is captured in their book:
Hyde, R. & Edwards, J. (Eds.) (2013). Mentoring mathematics teachers: supporting and inspiring pre-service and newly-qualified teachers. Abingdon, UK: Routledge.
Theory (Hidi & Ainley, 2008) suggests that interest encourages self-efficacy through prolonged engagement with materials: i.e., you like/value/enjoy it so you do more, so you improve? The connection is almost certainly reciprocal, but this is what theory suggests is the key line of development?
How does this fit your practice (teaching/learning) or other theories in this or parallel areas?