On the first day I do a series of discrepant event demonstrations. There are about 8 of them - I can describe them another time - and I like them because they fun and interesting on the first day of school. But there is more to a good demonstration than entertaining the kids.
Too often traditional science teachers do demos as a "show-and-tell". Where they do a demo and then launch into a full explanation of the science involved. Even worse are the teachers who do a demo and then they challenge the kids to explain the science with no context or models to apply.
Current research into demos shows that these methods are ineffective. http://bit.ly/PGSRxv
"We ﬁnd that students who passively observe demonstrations understand the underlying concepts no better than students who do not see the demonstration at all, in agreement with previous studies. Learning is enhanced, however, by increasing student engagement; students who predict the demonstration outcome before seeing it, however, display signiﬁcantly greater understanding."
So here's what I do:
First I describe the event (without the outcome).
Next I ask them to predict the outcome (I like to give them multiple choice).
Then they have to vote! I mean they really have to vote - out loud, in front of their peers.
Once they've all committed to their votes I do the demo.
At this point I don't care about the actual answer. Its all about engaging the students in their own learning. This really sets them up for the whole class. There are no answers from me - you've got to figure it out for yourself.