Critical Thinking: A Path to College and Career is an excellent article from Edutopia which contains numerous resources on using the Socratic Method of questioning to increase critical thinking skills. The article focuses on how KIPP King Collegiate High School in San Lorenzo, California uses critical thinking to prepare students for college. They use the Socratic Method in order to help promote critical thinking skills. The Socratic Method gives students a chance to process and verbalize their learning by formulating and discussing questions related to the content. The Socratic Method is not widely used in math, but it can be a great way to sum up a unit or an alternative assessment.
If you're interested in learning more about the Socratic Method, make sure to view the Free Resources and Tools section that accompanies this article. They have included some excellent rubrics, planning guides, etc.