Show Design Patterns in Examples
There where some plenty good answers, alright. I also think, that you should use good languages, good, skillful examples, but I have an additional suggestion:
I have learned what OOP means, by studying Design Patterns. Of course, I have of course learned an OO-language before, but until I was working on Design Patterns, I did not understand the power of it all.
I also learned much from OO-Gurus like Robert C. Martin and his really great papers (to be found on his companies site).
Edit: I also advocate the use of UML (class diagrams) for teaching OO/Design-Pattern.
