With a two-pan balance? With a timer? With a thermometer?
Using a ruler, fourth graders measured the distance a paper clip would "jump," or be attracted to a magnet. They engaged in rich discussion as to what each distance they measured meant, and they came to the conclusion that the greater the distance a paper clip could "jump" meant that the magnet had a greater magnetic field. Magnets whose magnetic field was weaker meant a paper clip would have to be pulled closer towards the paper clip to be affected by the magnetic field. Awesome experimenting fourth grade!