Many people who teach ballet don’t know much about the history of this art form. Here is a good resource from Northeastern University that provides some of the background–reaching all the way back to the courts of Renaissance Italy.
This site is definitely worth a quick read to brush up on the details if you plan on teaching. It is also a great primer for dancers who have not yet learned about the art form that they are practicing. I found it to be conscise, yet quite detailed.