The British documentary company, Pathé collected documentary footage which played before movies in theaters during much of the 20th century. Those films have now been released for free use (what a social studies boon!) on YouTube. If you have been angling to get YouTube approved in your district, this may be the event which will do the trick.
Thanks to Nate Everett, @ThalesDream on Twitter, for the alert about the OpenCulture Article. http://www.openculture.com/2014/04/free-british-pathe-puts-over-85000-historical-films-on-youtube.html