Stellarium, a free planetarium software, is the perfect tool for teaching an eclipse. Teachers can simulate a sky from any location at any time. As our school system prepares for the total solar eclipse, we are using Stellarium to show students what they should expect to see outside. Students will be able to understand just how dark it will be and will know how to spot planets that become visible. It (along with NASA TV) also provide a fallback plan in case of cloudy weather.
The directions below show how to deploy and configure Stellarium. At the bottom is a small user guide that you can modify for your environment.