The teacher goes into class and was determined to find out what they students knew about the functions of the heart? He asked the students to each tell him what they knew so that they could decide what they next wanted to know. This was not just serendipity, he wanted wanted and waited for them to recall what they knew.
Could I afford to do that in a class of 35-40? How long will it take for me to check that everyone was on the same page? Will it be easier to take the responses from the vocal knowledgeable few and assumed that therefore everyone knew? It would be easier but was it educational? How about the silent minority who knows just as much if not more? How about those who knew a little less and felt their views were not important anyway as someone else would have said what they wanted to say?
I think it is important to check what they students know. The more important question, without becoming metaphysical, is how do I know what they really know? Is it based on a few answers? Can I safely correctly generalise for everyone else?
Evil or necessary, in a big classroom with 40 student, the next most effective way to ensure that everyone knew something is for me make sure they knew the same things. The efficient way to ensure that everyone knew the same things is to tell them what I want them to know. The inevitable way to ensure that I tell them what I want them to know, is to ask the question and answer my own question. This is the evolution of didactic teaching.