I am working with several of our District's Environmental Science teachers to create a GIS lesson plan. None of them have GIS experience so I am taking the lead. I was going to make Salmon the focus because of the abundance of data on the animals and the natural resource they use (calfish.org, California Land & Water Use , and California Data Exchange).
I was going to start with an intro on what GIS is with links to useful resources (ArcGIS Resources and GIS Stack exchange).
Then show where I got the data from but have it primed and loaded on ArcGIS online for them to actual do some mapping. Maybe have them create some web mapping application? One showing where Salmon critical habitat is, where the monitoring stations are and how landuse/water use has changed? I think that web map with the comparison slide has a nice "wow" factor for high schoolers.
What have you used with students that seem to really help convey the principles behind GIS? I always reference the "Yelp" app on my phone. Lots of attributes (rating, menu, name, food genre) tied to a location (restaurant address) and can be queried by location and attributes.