**Line symmetry**:

I drew the left half of a cartoon butterfly on the whiteboard, right next to the seam between the two boards at the front.

“Did I draw the whole thing?” (“No, duh”)

“Do we know what the whole butterfly looks like?”

“Okay, someone come up here and draw the rest of it.” Girl comes up and draws – a few rowdy kids point out everything she’s doing wrong – ‘That part’s too small! That doesn’t look right!’

“Okay, so you were correcting her – how did you know that it was wrong?”

Students already know line symmetry, intuitively. The only thing they need to learn is how to understand what they already know a little more deeply, so that they can apply it in less intuitive situations. This has kind of turned into my theme for the geometry unit, actually. Half of what I’m teaching them is stuff they already know without thinking about it.

**3D Surface Area:**

I pulled out the straws and tape for this one. Groups of students built the five platonic solids and had to calculate the surface area of each one.

(The trick is to get bendy straws and cut along the short end of the straw, so that it can be pushed together a little smaller and tucked inside the long end of another bendy straw. You can build the 2D shapes for each face without using any tape at all. Then you just tape together the faces.)

This … kind of worked. Students generally had no problem getting that the surface area is calculated by finding the area of each panel / face and then adding them up. (One group had a moment of difficulty, but only because I brainfaded and said “length cubed” instead of “length squared” and confused them for a minute.)

I experimented with letting students choose their own group after having told them which shapes would be more challenging – sort of self-selecting a difficulty level. I warned the “easy mode” groups that once they were done they’d be helping the harder groups finish their constructions. Unfortunately, of the two harder shapes, one group blitzed through it and the other group was stubborn and wanted to do it themselves. The groups were also a bit too large at 5-6 kids per group. This might be worth trying again, but only if I can frame the tasks so that “easy mode” doesn’t also mean “takes a lot less time”.

**Photoshop:**

We have a collection of links to online tutorials that we use to get the students up to speed on most of the key tools available in Photoshop. For the healing brush we send them to this one, where there’s a close-up of a guy’s face that they’re supposed to “fix”.

Students started asking me what they were supposed to fix on the photo. “His nose?” “There’s nothing wrong with his face.”

I had no way of explaining that one quickly without feeling like an accomplice to something horrible. I had no choice but to pull up the Dove “Evolution” video and spontaneously add a new goal to my unit: to have them understand that the media around them, especially advertisements, are full of images that look absolutely nothing like reality. I went just a little Adbusters-ranty on them. I replayed the second half of the video a couple of times so that students could wrap their minds around just how much evil is done with Photoshop in the name of increasing sales.