Read David Swenson's reply:
Without knowing the precise complaints or seeing the full picture, it is difficult to give specific advice. But I can say that it requires a great deal of patience to teach yoga. We all carry our unique personalities and emotional makeup into every facet of our lives—including yoga class. Yes, yoga practice can foster calm, focus, and balance, but this could take years or even a lifetime. I tell students that when practicing yoga we must think in terms of decades.
As teachers, we must see ourselves as the servant of the students. Our duty is to present the practice in a manner that the student can understand. Just as we encourage patience in our students, we must also foster patience in ourselves as teachers. Growth as either a teacher or a student is like the growth of a tree: The strongest trees in the forest grow the most slowly. The students that you are having challenges with are coming to class, and that is a big step for many people. Let the yoga do its work over time, and do your best to nurture the growth of the students.
David Swenson made his first trip to Mysore in 1977, learning the full Ashtanga system as originally taught by Sri K. Pattabhi Jois. He is one of the world's foremost instructors of Ashtanga Yoga and has produced numerous videos and DVDs. He is the author of the book Ashtanga Yoga: The Practice Manual.