Thursday, November 22, 2007

Lessons on Lessons while Cooking Mashed Potatoes

I hope you had a wonderful Thanksgiving. We had a wonderful time here. We didn't go anywhere we stayed home, my Mom came, and we cooked here. As often happens, while discussing making mashed potatoes with my wife, I had a little epiphany. Maybe it isn't an earth shattering discovery, but I love a metaphor and I think this is a good one, so bear with me and I think you find a story that all teachers can use with their students.

As I said we made Thanksgiving dinner here this year. My wife picked the recipes, and it just happened that we picked all of our recipes from a cookbook we have from America's Test Kitchen. One of the things that we love about this cookbook is that it tells you their theories about "why" they do things. My wife were talking particularly about the mash potato recipe. I am sure that many of you know this, but it is important to add the butter BEFORE the milk. This has to do with "coating starches, etc., etc.", and my wife noted that it was not something she knew about. I told her that I had shared that same information, about the butter before the milk, with my wife's mother. My mother-in-law seemed to think that this was not interesting news of any sort, but something everyone knew. Of course, her own daughter didn't know it.

What does this have to do with teaching math. We often show students what to do. And often we are surprised by the ways they fail to do what we show them. But in this example my wife watched her mother make mashed potatoes many times, but because she didn't know why the butter went in before the milk she didn't know that there was any importance to the order. Since then, my wife has been mixing mashed potatoes, milk, and butter all at the same time. The Horror.

Well the mashed potatoes were great, and I believe that my classes will be improved because I have been reminded one more time that the model of teaching math where you ask students to just do what you do, and not show why is forever deeply flawed. Why is it flawed? Because it leads to lumpy mashed potatoes.

More secrets of mashed potatoes here.