Online course discussion is an excellent opportunity for teaching and prompting critical thinking. By presenting challenging open-ended questions, you can engage in a sort of asynchronous Socratic questioning with your students. 

Use the following framework to structure your discussion questions or prompts. 

• Provide a setup. Present a statement, observation, or scenario that requires students to reexamine or apply what they're learning.   
• Ask students to commit.  Ask a specific question, one that won't have an obvious right answer, likely in one of the following categories. 
  • Personal reflections: “What do you think about ___?” “How do you feel about ___?” 
  • Past experiences: “In the past, how have you responded when ___?” “Have you ever had an experience where ___?” 
  • Rational conclusions: “What conclusion do you draw from ___|?” “Of ___, ___, or ___, which choice makes the most sense given ___?” 
  • Process or order: “How would you go about ___?” “In what order would you ___?” 
  • Guesses or estimates: “What would you do if ___?” “What might have happened if ___?” 
  • Superlatives: “What is the worst approach to ___?” “What is the most appropriate ___?”  
• Ask students to defend their commitments.  Give students clear directions for defending or explaining their responses. 
  • "Why?"  
  • "Why or why not?" 
  • "Explain your reasoning." 
  • "Defend your response through one of the theoretical frameworks in this week's reading."
  • "Explain your response using data from this week's field observations." 

See also: 

MacKnight, C. B. (2000). Teaching Critical Thinking through Online Discussions. Educause Quarterly, 23 (4), 38–41.  

Murchú , D. Ó., & Muirhead, B. (2005). Insights into Promoting Critical Thinking in Online Classes. International Journal of Instructional Technology.