Why does a compass always point north?

Why does a compass always point north?

Investigation
The children started by making a simple ‘wet’ compass. First, they magnetised a sewing needle by repeatedly stroking it with a permanent magnet. Children then slid the needle inside a trimmed drinking straw that is floating on a saucer of water. They observed the straw and needle to see if they point north. Children then identified what happens when they move a magnet and other materials, such as metal, plastic and wood, close to the straw and needle. Finally, the children were challenged to improve the design or accuracy of their compass by choosing a variable to test.