I am currently reading Otis Webb Brawley's How We Do Harm: A Doctor Breaks Ranks About Being Sick in America (New York: St. Martin's Press, 2011) He gives an account of his Jesuit education and the important lesson of Father Richard Polakowski, a beloved high school teacher at the University of Detroit Jesuit High School. "Polo," as the students called him, "had a maxim that no student who took his class could miss: 'Say what you know, what you don't know, and what you believe--and label it accordingly.'" (p. 75)
Use your intellect, gentlemen. Start with knowledge, find its boundary. DO not stop! Save room for belief, but examine it fearlessly, for genuine examination knows no limitation. (p. 75)
Dr. Brawley has used this lesson in his distinguished medical career, and I think we can take it right back to the classroom. Students should examine what they know, consider the limits of their knowledge, and press a little beyond that to take a stab at an opinion and stand by a truly "educated guess."