Ask a child to hold up one magnet. To figure out how strong the magnet is, hang paper clips from that magnet one by one so that it looks like a chain. You could also try hanging more than one chain from a magnet. The magnet that can sustain the most paper clips has the strongest magnetic force. This is a concrete way for children to "see" magnetic force. Note to teachers: Spend some time familiarizing yourself with how this works. Play around with this activity before attempting to share it with your class.
How it works: Some magnets are stronger than others are. As you hang paper clips from a magnet, they take on some of the magnetism, thereby temporarily becoming little magnets. The magnet that can sustain the longest chain or the most chains has the strongest magnetic force. (Mailbox Magazine, Dec./Jan 1993-1994 p. 50)
Another way to assess at the strength of magnets is by looking at the different parts of the magnet. All magnets are strongest on their ends. Focus particularly on bar magnets and horseshoe magnets. First ask the children to test all the objects to make sure they are magnetic, and then challenge the children to try to pick up objects with the middle of the magnet. They will notice that the magnet will only pick up the heavier objects on the ends. (Mailbox Magazine, Dec./Jan 1993-1994 p. 50)