The Barcelona Field Studies Centre has developed a neat little compass tool that works with Google Maps. Google Compass overlays a compass on a Google Map. Users can drag the compass and position it to point in any direction. Users can then plot a route on the map using the compass. The compass tool will account for magnetic declination when necessary. The compass tool will also provide users with the coordinates of their routes.

Applications for Education
Google Compass could be used to teach students about the difference between magnetic north and true north. Students can position the compass on various places on the map to see how the difference between magnetic north and true north varies depending upon where you are on the globe.

Here are some related items that may be of interest to you:
Google Earth Across the Curriculum
Free 33 Page Guide – Google for Teachers
Using Maps in an Elementary School Math Lesson