This is quite possibly, the coolest thing I've ever tried out. The premise is as follows: a debate between two students (or teams) where four referees observe. The referees score what they see and a winner is announced at the end.
Now add in entrance music a la pro-wrestlers (think the Rocky Theme, We Will Rock You etc.) and run it on an open evening and I promise you this - you will have EVERY parent in at some point to see what is going on.
I've run this at SIX parents evenings now and the same thing happens every time - all of the kids rock up to watch. I set it last time round where the Deputy Head took on the winner of the students (a year 9 girl). They packed the place out to see who won . The debate topic "Batman vs Superman" (serious stuff this). Needless to say, she wiped the floor with him (in a totally professional way).
You'll need to be the promoter/commentator/ring side referee - this can be exhilarating and exhausting!