I have never taught in a school, just been a pupil. I do remember the sparring that goes on between pupils and teacher. The kids push ‘to the limit’. They then improvise just under this limit, causing trouble. My thought was that teachers could either define limits carefully or, to be slightly evil, just behave in an inconsistent manner. For the latter, think: random acts of terror! In this scenario, the kids can never quite work out any rules of engagement, and will sit there terrified in silence. Evil, I know.
I wonder whether this approach might be useful for learning outcomes. Rather than taking part in an evolutionary war between the students on one hand who want ever more explicit statements of what they should know, and on the other, the inevitable ignoring of all aspects of knowledge that cannot be explicitly stated, we should aim for a little more disorganisation. We shouldn’t tell the students what they need to know, and we certainly shouldn’t tell them the format of the exam, or even when it is. What do they need to know? Lots. Pay attention. Evil, I know.