Show students a set of materials cubes and tell them they will weigh the cubes in grams, just as they weighed the classroom objects. Remind students that grams are the units scientists use.

This will be the students’ first opportunity to discover how the weights of the cubes compare in terms of grams. Point students’ attention to the investigation question:

Let students know that more than one student will weigh each type of cube. Scientists want other scientists to try the same measurement or experiment, to see if they get the same result. This is one way that scientists learn if their work is accurate, or if they have made a mistake.

• Why do scientists want other scientists to try the same measurement or experiment?

Give every student one cube to weigh. As you hand each student a cube, ask them to think about or predict how much their cube weighs in grams.