[PSTUM-list] refs on TA training effectiveness?

This may sound like an obvious question, so I am hoping there are some obvious answers. A colleague of mine is helping NSF with a "What's Known From Research" report and realized she had no research citations to support the idea that graduate teaching assistants teach better and their students learn better if the TAs receive some kind of training or support. I think everyone believes it. I've seen a couple of theses about this issue discussed on the list. Can people who've done the literature review give me what you consider the best references addressing this specific question? Preferably with a sentence or two commentary on each... best wishes, Eric -- Eric Hsu, Associate Professor of Mathematics San Francisco State University http://math.sfsu.edu/hsu erichsu(a)math.sfsu.edu