What teachers are doing when they engage in "classroom discussion" is quite different from what is typically considered discussion. The purpose of classroom discussion is to enable the teacher to pull the content dictated by the curriculum out of the class by imposing a limited discussion-like format. Most everyone who has been in the American school system has experienced hour upon hour of these pseudo-discussions. In classroom discussion, the questions the "successful" student asks are the questions he knows follow the direction the teacher wants to take.
Other questions generally get gently put aside. Asking why, though, (when it's not clear that the teacher wants the question) causes trouble. Thus, we breed students who learn that there is a right next question, and if they're not sure what that question is, they are better off not asking anything. We breed students who therefore really become quite skilled at asking and answering only one question: What is it that the authority figures want me to do next?
Where am I in the content of the book?