what is the perimeter?
Posted by edunerd on May 21, 2008
I sat in a math class a few days ago and watched them take up a homework sheet from a couple days earlier. Several students had found the work difficult (and a few had forgotten about it), so the teacher had decided to discuss it with them instead of just marking it.
The sheet said, “Find the perimeter of the triangle.”
“How do we find perimeter?” asked the teacher. The students looked at her, probably waiting for her to answer her own question, or at least hoping that they wouldn’t be expected to.
“What do we need to find?” she asked.
One student said she didn’t know. Another said (not very confidently), “Lenth times width.” A few others agreed that multiplying the length and the width (of a triangle?) would give the perimeter. Someone may have suggested multiplying the base and the height.
The teacher asked them for the English definition of perimeter from their books. Instead of turning to the page that had the definition on it, the students stared back at her, wondering what it could possibly be that she wanted.
The perimeter of any two-dimensional object is the distance around it. This is something that 14 and 15 year olds should know. I am almost positive that all of these students learned what perimeter was several years ago, and I know for a fact that they were told again earlier this academic year (and again earlier last week), but they all treated it like it was new information. Or maybe something that they had been told long ago but had never heard about since then.
To be honest, I’m not at all surprised by this. I’ve seen (and heard about) high school students who are surprised to learn that when adding fractions, they need to first find a common denominator. The simplest operations become complicated once students reach a certain age. Math is sometimes a little tricky, so some of them figure that everything is incredibly complicated. What’s going on here? What is it about math that causes amnesia in people who are actually quite bright?
Students lose confidence, so they don’t try. Class is boring, so they don’t pay attention. Eventually, they get so lost that they couldn’t catch up if they wanted to.
This is not novel by any means (or maybe it is and I’ve just been listening to the wrong people), but math is taught wrong. Educators and policy makers need to get over the idea that students need to learn the basics of math before they can do the interesting, creative, fun stuff. The basics actually become fun when seen in the context of what math really is. None of the students in that class knew what the perimeter of a triangle was, and why should they? What interest is it actually to them? (And don’t start telling me that it has practical applications. If they need to know how much fencing they need to go around their yard, they’ll measure.)
Some of these students will probably graduate from high school with no clue what a perimeter is. They will go through the rest of their lives not knowing, and they’ll probably be fine. But they’ll also go through the rest of their lives not knowing how beautiful and elegant and exciting math can be, and I think that’s a real shame.
