We have used several books/leaflets to walk students through the critical thinking process.
The one we use for graduate students, I also used with my freshman seminar students and they seemed pretty intrigued by it... "Asking the Right Questions" by Browne & Keeley. We have a presentation based on it at our website at:
Another option is the Miniature Guide to Critical Thinking Concepts & Tools by Dr. Paul and Dr. Elder. You can find their book at: (the more you order, the cheaper they are...)
I personally like the first book better, and it came highly recommended from faculty in the public policy department here... But, these are two definate options.
My freshman students seemed shocked that could and should question everything they hear... That maybe things they have been told in the past might not be correct... It was an interesting lecture and I wish I could have delved into it more!

Melissa Thomas, J.D. 
Graduate Student Learning Assistance Coordinator 
Tomás Rivera Center for Student Success 
University of Texas at San Antonio 
One UTSA Circle 
San Antonio, Texas  78249 
Phone: 210.458.4691 
Fax:  210.458.4695 
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