The two question rule: ask a probing question, then follow it up with another question that requires deep thought to answer.
Using the two question rule we can extend knowledge to a deeper level and students will begin to anticipate that second question. This will give people the need to think deeper on a regular basis because they will want to be prepared for the next question. You don't even need to always ask the second question once it is anticipated.
Read the full article here: http://www.edutopia.org/blog/importance-asking-questions-promote-higher-order-competencies-maurice-elias
This article was brought to my attention by @thinklangley