I was talking to another yoga teacher about how to think of the difference between teaching and practice. I have always explained to myself that teaching is just articulate practice, that is, one’s own practice put to words. A teacher who can explain the details of a pose does so by discovering those details in her own practice. Assuming one has reasonable verbal skills, a teacher who cannot explain a pose well has not practiced well. All true, but there is more to it.
There is a significant difference between teaching and practice. In our Iyengar system of yoga, there is often high anxiety in the lead-up toward a certification assessment, where every few years one’s knowledge of a certain set of poses and one’s teaching skills are examined. The fretting causes people to practice for teaching, rather than practicing for practice. This is singularly unhelpful to the one going up for the assessment (truthfully, this phenomenon of practicing purely for teaching happens to many of us completely apart from the seemingly high-stakes issue of passing The Big Test). So what is the difference?
True practice in the Patanjali way is an inward-looking, inward abiding practice. If done well, it makes one silent both inside and out. Yogas citta vrtti nirodhah, for goodness' sake. Teaching is fundamentally unlike practice in that it is extroverted, outward-looking and outwardly reactive. The teacher must be looking for and responding with useful words and actions to what the students are doing in the moment. The insights and wisdom that a good teacher can express in class come from insight and wisdom gained in that inward-abiding practice, but in class she depends upon a sharp outward focus to succeed.
If a teacher teaches in the introverted way she practices, her students will never understand except from their own effort. In which case, why come to class? If a teacher practices only thinking outwardly, "How am I going to explain this in my classes?" she will never gain insight that comes from true silent witnessing. That teacher suffers both from an un-practice-like practice, but also from thinking more of a desired outcome than of the pose itself.