This is the best deal in homeschooling. From personal experience with SOS: When you register your license, you are allowed 5 students to use the same license. This way, you can teach multiple grades in the same year. You only need to register the license once, then write down the activation key and use it if you ever have computer problems and need to reinstall.
If you bought more than one subject, you actually have the ability to register a license for each subject. Say you have 10 students, you register one license for the first computer for use by the first 5 students. Then you register the second license for the second computer for use by the next 5 students!