This is a question I ask myself often as I teach school. I came to the conclusion a number of years ago that the person doing the most work was the person learning the most. Usually teachers know their material so well because they've worked so hard on it.
But I've found that, in teaching, once a teacher masters the material, it is best to find assignments and exercises that make the student work, and not the teacher. More and more, I search for things for my students to do that require little of me (especially in grading effort) but force them to dig deeply into the material.
Examples: memorization. Memorizing and reciting poetry require quite a bit of work for them, but the grading on my part is as simple as listening to them recite, and writing down the grade. I deduct points for errors as they recite.
Another? Quotation hunts. I amass a list of important quotations from a play or a longer work, type them on a sheet, rearrange them, and then require the students (working in groups) to put them in the correct order, and write the speaker's name as well. It takes them a class period to do it, they compete for which group completes it first, and I can use those same quotes on their test. It's a great review strategy.
I have other exercises, but you get the idea. Good students love to work, because they can feel their minds being exercised and energized. There is no reason for a teacher to wear herself out. Of course, teaching with this kind of "ease" requires the teacher to master her material ahead of time. But in the classroom, it's always best to see the students working away like little ants, and the teacher smiling happily as she watches them do so.