Sometimes the greatest compliment to a mentor is becoming capable of disagreeing with them intelligently.

Someone who can disagree with you well has absorbed the reasoning rather than the conclusions. They have enough of the framework to use it against you, which means the teaching went all the way down. Agreement is easy to produce and proves very little. Intelligent dissent proves that something real was transmitted.

When someone you have taught pushes back, listen for whether the argument is sound before defending the position. If it is, say so plainly. That moment is the result you were working toward.