A sensitive approach towards your students can prevent many problems. If you phrase questions and criticism carefully, you can generally avoid defensive or hostile responses. If you are supportive, encouraging, and respectful of student ideas in class, then you can correct wrong answers, point out feeble arguments, or highlight weak points in a positive manner without discouraging your students. Rather than asking what is wrong with a written paragraph or a problem solution, ask how it could be improved. Instead of asking what the weak point of an argument is, ask how well it applies to or uses the material for the session. Rather than dismissing an idea immediately, ask the student to clarify it using the material for the session. At the same time, it's important to maintain your credibility. Don't, therefore, respond to student questions with "good point" when the ideas are in fact poorly presented. Always show students the courtesy of fully attending to their answers when they offer an idea; don't use that time to write on the blackboard or scribble on a note pad.