A few years ago, when I decided to get serious about teaching magnetism, I
finally figured out a problem that many of my students had. They thought
that the "North" side of a magnet was the side of the magnet that was on
the north -- geographically -- side of the magnetic.
Looking back at the text and the order of how I taught the material, this
interpretation wasn't all that unreasonable. I had spent more than a bit
of time discussing how iron could be magnetized by the earth's magnetic
field, and so on.
Now, I teach magnetism differently. In the students' investigations they
discover that each magnet has two ends*. Picking one end, it is attracted
to one end of another magnet and repelled by the other. The other end
behaves similarly but in reverse. The end that used to be repelled is now
attracted.
I ask the students to come up with way to identify their magnet ends,
offering sides "A" and "B" as options. Soon they notice that one group's
naming convention is not always the same as their own, and so they often
fight for a standard.
When we do compasses they realize that the earth makes a handy standard.
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One interesting side note. Most of students have already heard that
opposites attract and they have dealt with static electricity, too, so
they use a formulation like "A attracts B and repels A." Some students try
to come up with a system where the naming is like "Tab A goes into Slot
A." They never get far, but a few students try this every year.
Marc "Zeke" Kossover
The Hockaday School
*I don't give students multi-pole magnets until very late. Do I look like
a jerk?