I was recently hired by a summer enrichment program for 4th-12th graders to teach several dance classes, one of them called, "DanceSport: Dance your way to Fitness." I understood this to be a dance aerobic class, which fits more with my dance background, but no-- it's a ballroom class! I have had great fun searching out resources-- I even took a private waltz lesson this week-- but am clueless about how to best structure the class. I'll have 4th-12th graders all together for an hour a day, 5 days/wk over a 3 week session. Any suggestions, however brief or informal, are coveted!

That's a tricky situation. What you'll probably find occurring is that some of the parents of the kids will have some ballroom dancing knowledge and they will figure out rather quickly that you are not qualified to teach that. But you should probably try to learn as quickly as possible the basics to the Waltz, Fox Trot and Swing, and maybe the Rumba.
You can do part of that by watching the dance step videos on this site, or ordering a couple of the DVDs.
But it won't be easy. You really need to know the best music, all of the framing and posture techniques, etc.
But again, this site can help with a lot of that. Plus, in a summer class like that, real basic stuff -- like a box step and a couple of turns -- will probably suffice.
If you don't have to stick with a true ballroom session, just ask the kids what kind of music they like, and then see if you can arrange something along the lines of a ballroom step sequence to their music ... something like that could take the better part of a week!

Good luck.