Design and run a fair test showing that magnetic force gets weaker with distance and that different magnets can have different strengths.
Magnetism is strongest right up close to a magnet and gets weaker the farther away you move, until eventually it is too weak to feel or see at all. Different magnets also have different strengths: a small, weak magnet might barely lift one paperclip, while a strong magnet can lift many paperclips, or even work through a barrier like paper or your hand.
To compare magnet strength fairly, you have to run a fair test: change only ONE thing at a time, like the magnet itself or the distance, while keeping everything else, such as the paperclip type and size, exactly the same.
Mastery looks like: They design and run a fair test that shows magnetic force weakens with distance, and can compare two magnets' strength fairly.
Common stumbles: Changing more than one variable at once (like both the magnet and the paperclip), which makes the test unfair and the result unclear.