At Harvard, Twersky taught both undergraduate and graduate students. His popular course, "Moderation and Extremism," which compared and contrasted the paths to virtue in the works of Aristotle, Maimonides, and Thomas Aquinas, drew over 200 students in 1995, the final year it was taught. Over the course of his thirty years at Harvard, he taught a large number of graduate students. His exacting standards and expectations were legendary. Nevertheless, over thirty individuals completed their doctorates under his guidance. Many of these play leading roles in Jewish studies, both in North America and in Israel. Among these are Morris (Moshe B.) Berger (Cleveland College of Jewish Studies, Edward Breuer (Hebrew University), Bernard Dov Cooperman (University of Maryland), Joseph M. Davis (Gratz College), Lois Dubin (Smith College), David Fishman Jewish Theological Seminary, Talya Fishman (University of Pennsylvania), Roman A. Foxbrunner, Daniel Frank (Ohio State University), Steven Harvey (Bar Ilan University), Carmi Horowitz (Michlelet Yerushalayim, Jerusalem), Eric Lawee (Bar Ilan University), Diana Lobel (Boston University), David Malkiel (Bar Ilan University), Allan Nadler (Drew University), Ira Robinson (Concordia University), Marc Saperstein (Leo Baeck College, London), Mark (Meir) Sendor, Jacob J. Schacter (Yeshiva University), Bernard Septimus (Harvard University), Marc Shapiro (University of Scranton), Michael Shmidman (Touro College), David Sklare (Machon Ben Zvi), Gregg Stern, Adena Tannenbaum (Ohio State University), Joshua Levisohn, and Jeffrey R. Woolf (Bar Ilan University).