"If teaching were the same as telling, we'd all be so smart we could hardly stand it." (Mark Twain)
This is how Spencer Kagan, well known among educators for his contributions to cooperative learning, begins his article "Tellin' Ain't Teachin': The Need for Frequent Processing." In the article Kagan explains how the brain responds when asked to learn new material and what happens when there is insufficient time to process newly received information. One way to ensure that "processing" occurs is by giving students frequent opportunities to discuss and think about the content. Anyone who is not convinced, or anyone who wishes to convince colleagues of the power of student discourse for learning mathematics, should read this article.
And in case you have forgotten, SU HU PU stands for Stand Up, Hands Up, Pair Up!
Read the article here: http://i-a-e.org/newsletters/IAE-Newsletter-2012-98.html