There are endless classroom uses for Google Earth. One of the coolest features is the measurement tool. I have found it accurate to the inch. Amazing.
The first time I saw this a couple of years ago a friend said, "I hope you don't have to go to the bathroom, because when you see this you're gonna wet your pants." Now it seems downright commonplace. A classic example of how quickly technology gets integrated into our lives.
Try playing around with elevation to make it even better.
These Google Lit Trips are a perfect educational use of Google Earth.