Do you use soft iron bar magnets in your classroom magnetism activities? Of course you do! Have you noticed their tendency to lose their field strength as time goes by? Such is the nature of soft iron. The fact that it can be easily magnetized makes it vulnerable to the loss of its field strength.
That's where a magnetizer comes in handy. I've got one that I use and am generally happy with. It's made by Electro-Technic Products (ETP), a company in Illinois. It's easy to use and works effectively.
There is one problem with it, though. One that American River College physics instructor, Ann Hanks, pointed out a few years ago.
The ETP magnetizer has its magnetic poles labeled backwards. The end of the magnet you place in the "north"-labeled receptacle will be magnetized south, and vice-versa.
Hanks pursued the matter and contacted the company. They were aware of the situation, but intended to maintain the errant labeling. ETP told Hanks that their customers complained when the "North" of their newly magnetized magnets failed to attract the north-seeking end of their classroom compasses. These customers wanted north to attract north.
ETP acquiesced and relabeled their magnetizer to match customer demand. "The customer is always right."
Well, except when they're wrong. If you get one for your classroom, you will need to relabel the pole indicators on the device before you use it. Sigh.