They (not surprisingly) offer no explanation as to what may have been behind the striking difference in post treatment testing between the groups, but they do offer three near breath-taking observations ". . . Gesturing can be a very beneficial tool that is completely free and easily employed in classrooms . . . I think it can have long-lasting effects . . . Teachers in the United States tend to use gestures less than teachers in other countries."
The study used "deictic" gestures (pointing at something physically present or conceptual). It is still an interesting piece of evidence. (They could, of course, have tested the main effect by having another group that did not see a gesturing instructor but were, instead, provided with left or right pointing graphic arrows superimposed on the screen.) Just thought I'd point that out . . .
In AH-EPS all pedagogical movement patterns involve deictic anchoring in the visual field as well. That has to count for something, eh?