New Lecturer

A new lecturer walked into a class one morning and after greeting the students, he asked, "Do you know what we are going to be teaching today?"

The students all chorused, "No Sir!"

Then he said, "Then there's no point teaching you what you don't know." and he left.

The next day, he came in and asked, "Do you know what we are going to be teaching today?"

They all answered, "Yes Sir!"

Then he said, "Then there's no point teaching you what you already know." and he left again.

The third day, he came in and asked again, "Do you know what we are teaching today?"

Then the students answered randomly, some saying yes and some saying no, then the lecturer said, "Those that know should teach those that don't know", and he left.