A couple of years ago I met one of America's great genealogists, Helen Leary in Toronto where she was speaking to the Ontario Genealogical Society. One of the topics she touched on was teaching beginning genealogists. Her comment was that she would in their first lessons teach these concepts: sources, information and evidence using the records of their own life! Later that weekend I was fortunate to have a late lunch with her and discuss this idea some more. I'll be exploring my thoughts on this issue but to start I would suggest some reading on your part.
Donn Devine, "Evidence Analysis" Professional Genealogy, A Manual for Researchers, Writers, Editors, Lecturers and Librarians. (Baltimore: Genealogical Publishing Company, 2001) 329-342
Elizabeth Shown Mills, "Working with Historical Evidence: Genealogical Principles and Standards" National Genealogical Society Quarterly 87(September 1999) 165-184
Thomas W. Jones, "A conceptual Model of Genealogical Evidence: Linkage between Present-Day Sources and Past Facts", National Genealogical Society Quarterly 86 (March 1998) 5-18
Do a little reading and watch this space for some of my thoughts on these concepts and how to teach them.