Questioning the Practical Nature of CP (yet again)

At the conference last weekend, Carol Richardson's paper on social justice introduced many ideas that are very similar to what we are taught in our critical pedagogy classes at Westminster. While most of her ideas made sense to me, I am having a difficult time seeing how this particular quote could be put into practice: "Only ask students questions when you do not know the answer and can learn something new from the students' answers." While this (and many other ideas at the conference) sound great in theory, I do not see how a teacher could implement it into a classroom. Yes, the students come to the class with knowledge and the teacher should understand that, but how can a teacher give students skills without actually giving some new knowledge?