I think this site may have been brought up in the past, but a great resource for classroom wargames is:

http://www.juniorgeneral.org/

Simple, rules, that can be modified easily, and easy to make components.

Pete Pelligino, a contributer to the site, has used the simple rules to run "cocktail party games" on the parque dance floor at the O-Club here in Newport to commemorate Trafalgar, Midway and Tsushima.