Constructivism vs. Realism in the Classroom

In class today, we discussed the differences between radical constructivism and realism in evaluating and observing the characteristics of an apple. How do these differences relate to teaching in a classroom? Let's look at the example from Dewey Dykstra's article on the tests of physics students. Teachers who chose the realist approach to teaching expressed the "facts" as they are, while the students memorized these "facts" as truths, and regurgitated the information on an exam. After the test was taken, the students showed no real understanding of the material. However, had these students questioned what they were learning and had their teachers encouraged them to draw from their past experiences, these students may have left the course with a comprehensive understanding of the material. In class, we decided that constructivist teaching emphasizes understanding over simply knowing. Constructivism also allows us to keep in mind that there exists information about everyday objects that we can never truly know. This relates back to Korzybski's idea that you can never know "all" about something. We can only know what our perceptions tell us. So, my question is: Do you believe that the constructivist philosophy should be introduced in the classroom, and if so, at what age is most appropriate for handling this higher-order thinking?