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Forwards and Backwards redux

So that lesson on multiplying negative and positive numbers still worked great for my algebra kids, understanding wise, even if they looked a little nonplussed at the end of it1.

As a recap, it goes through various combinations of video of a student walking forwards, or backwards, and then running the video forwards and backwards. forwards, of course, equates with positive numbers (and is carefully constructed on the video to go from left to right, to match our internalization of the numberline), while backwards equates with negative numbers.

The final slide has all four variations of the video looping at the same time, arranged in the usual +/- lattice. I have the kids draw the images, and write an analysis of what they saw.

This year, though, I added the coup de grace question:

What would happen if I took some video of that screen from here at the back of the room, and played that backwards for you? What would the math representation of that be?

And all of a sudden, they get that you could do this over and over again, and that every time you multiply by a negative number, you’re just flipping the sign back and forth…

1 Apparently I teach weird. They don’t seem to be used to having someone show them some stuff, and ask them to find patterns without much explanation on my part. I wasn’t aware that this approach was unusual. I don’t want to change it, but I should probably find a way to manage their expectations of how a math class works.

{ 2 } Comments

  1. Sarah | September 12, 2008 at 6:01 am | Permalink

    Let us know if you find a good way to manage those expectations of how math class works. I’m running into the same troubles and haven’t figured anything out yet.

  2. Mr. K | September 12, 2008 at 6:03 pm | Permalink

    Two days later, I’m not sure I need to.

    If you take dan’s advice to never let them put you in a box, this set of expectations about how you’ll teach is a couple months of freebie keeping them off balance.

    They think it’s weird, but I’m the only teacher who’s shown them 4 different (albeit related and poorly produced) videos all at the same time. That’s enough to get them to show up the next day wondering what in the hell I’m going to throw at them.

    It helps that I treat their time with respect, and make a big deal out of being productive during class time. That way, when I’m letting them struggle with something for 5-10 minutes (eventually to become 30-40), they know that I, at least, think it’s an important and worthwhile thing for them to do.