If your students are heading into midterms, or if you are trying to figure out your next "serious" lesson...how about teaching your students a dance?
In the States we are really big on shuffle and hustles, so I taught my students the "Cupid Shuffle."
The Cupid Shuffle is a VERY simple dance, and your kids will most likely catch on pretty quickly.
If you don't know it, here's the instructional:
http://www.youtube.com/watch?v=iJQKBk4oDr4&ob=av2nI would recommend that you learn it first and teach it to your kids rather than showing them the instructional. I think the instructional might be hard for them to follow (too much commentary).
Here's the music for your class:http://www.youtube.com/watch?v=fAhXfcm_v40When you play the music the first time, start it at the chorus (1:20) so your kids get a feel for the song while listening to what to do as they dance.
My friend tried this, and some of her kids finished early. She recommends having a dance off if you have a really active group, and/or teaching them another dance like the macarena or the electric slide.
Remember to have fun! If you teach with a coteacher, try to get them to dance too. The students should love it, and if they're shy, it'll get them motivated.