There is no real difference between mentoring and instruction - both are means to pass on knowledge and skills and both require mutual respect to be effective.
It is only those that insist on the more formal methods of instruction that become ineffective and rely on status to ensure the 'gradient' rather than it being self-evident from both the quality and quantity of the knowledge being passed along.
The best post I have read here in a long time!
Instructing is a form of art, or gift, that should not be squeezed into standardised procedures. Different students learn best in different ways and it up to the instructor to find this best way. The old military style might work in operational training, but for basic tuition there are better ways.