Students compare objects by holding them, using balance scales, or simple intuition to determine which is heavier or lighter. Language like 'heavier,' 'lighter,' and 'about the same' are introduced before standard units like pounds or grams.
You already know how to compare quantities — more, fewer, the same. Comparing weight works the same way, but instead of counting objects you are comparing how hard gravity pulls on them. Pick up a stapler in one hand and a pencil in the other. You can feel which one pulls your hand down more. That pull is weight, and without any ruler or scale, your body is already measuring it.
The most useful tool for this kind of comparison is a balance scale — two pans connected to a central pivot, like a seesaw. When you place an object on each side, the heavier side sinks and the lighter side rises. If both sides stay level, the objects weigh about the same. Notice you don't need any numbers at all: the scale is making the comparison for you visually, the same way a number line helped you compare quantities earlier.
The key vocabulary here is directional: something is heavier if it takes more force to lift, and lighter if it takes less. A backpack full of books is heavier than an empty one; a feather is lighter than a coin. These words describe a relationship between two objects — not a fixed property of one object alone. A watermelon is heavier than an apple, but lighter than a car.
Before you can measure exactly how many pounds or grams something weighs, you need this foundational step: placing objects in order from lightest to heaviest and checking your guesses with a balance scale. Measurement with standard units (which comes later) is just a more precise version of what you're already doing — replacing "heavier" with a number so you can compare things you can't hold at the same time.