There's not a whole lot to this idea, but it was a good opener for the quadrilaterals unit, and it was a good use of our whiteboards.
One of the things that I'm trying to be more sensitive to in Geometry is just how difficult vocabulary is for students. I feel as if a lot of teachers in my life taught vocabulary as if the hard part was keeping the connection between the concepts and their names straight. That's wrong, though. What's difficult about learning a new term is for the concept to make a clear and distinct impression upon the mind.*
* "Clear and distinct impressions" is for all my ex-philosophy major brothers and sisters out there.
Anyway, learning vocabulary. It requires real conceptual clarity before we can even talk about these things, let alone prove things about them, and so it's worth the extra time to get those concepts clear.
And it's also important to get the interconnectedness of these shapes clear -- that's a major theme of this unit.
Anyway, start by introducing the concept of a family tree. Know your audience. My boys know about video games, so we drew three big circles containing the words "Sony," "Microsoft" and "Nintendo." They told me video game consoles made by each of those three companies. When we got "Playstation" on the board I asked them whether there were different types of Playstations. Yeah, there are. And all of those things are Playstation machines, and all of those are Sony consoles, etc.
Then they made these.
Nothing ground-breaking here, but it was a good activity.