Like pretty much everyone who's posted, my teachers played during lessons. Some gave more explanation to what they were doing (or thought they were doing) than others, but I find now that I often don't remember those explanations unless I wrote them down or recorded them. However, I can always remember the sound. My primary teachers: Scott Thornburg, Stephen Burns, and John Rommel all have very distinctive sounds that stay with me, but this is also true for people I've studied with for shorter periods. On a slightly different note, I have to say that I've had to work very hard in my own teaching to figure out just what and when to play for my students, in that making a positive impression is very important. If I step on something, whether difficult or easy, it's not very helpful to the student. Essential to this point is the idea of really listening carefully to them and being able to hear exactly how their playing differs from how "it should go", or to hear the musical alternatives to their rendition. If this is clear in my own mind, then demonstrating is easy. However, it really saps my energy and after two/three hours of teaching I'm mentally tired. Also important is the Arnold Jacob's idea of teaching being a "different hat" than playing. If I'm trying to explain something while playing, it usually results in a mistake. Switching back and forth between the playing and teaching "hats" is really challenging. My respect continues to grow for those teachers who've mastered the ability to play in lessons!