Skeptics virtually universally endorse teaching critical thinking skills and concepts at all educational levels. Following are some suggestions for tools to use to aid in this goal:
How To Think About Weird Things: Critical Thinking for a New Age by Theodore Schick and Lewis Vaughn. Although this book is several years old, it continues to get excellent reviews from those knowledgeable in the subject and many recommend it as an initial introduction to critical thinking.
Hemant Mehta recommended several resources recently on his blog.