Many high school educators are looking for examples of "teaching a GIS class". Not "teaching with GIS" but "teaching about GIS," as one might teach CAD or digital art or video editing or computer science -- the technology as the class. If you are already doing this, please comment here about the focus of your class, what questions you have, what resources you are using, and how it is going for you and the students.
Here are some important publicly visible resources worth paying attention to: