According to a new paper by Richard Vedder and two co-authors using University of Texas data, 20 percent of professors teach 57 percent of student credit-hours — and still do their fair share of research (they bring in 18 percent of research dollars).
The wrinkle here is that the methodology gives a lot of credit for teaching huge classes — three hours of teaching a class of 20 students is worth the same as a single hour with a class of 60, so far as I can tell. As students branch out into different areas of their fields, they need to be taught in smaller groups, which by definition means less “efficiency” as measured this way.