What should sixth-grade students already understand about the concept of work?

The correct choice emphasizes the fundamental definition of work in physics. Sixth-grade students should understand that work occurs when a force is exerted on an object that results in displacement. This means that simply applying a force is not enough to constitute work; there must be movement in the direction of that force.

This understanding is crucial for grasping broader concepts such as energy transfer and mechanical systems. For example, pushing a box across the floor involves both a force and a movement, therefore fulfilling the criteria for work. Conversely, if a student pushes against a wall with all their might but does not move it, they are applying force without doing work in the physical sense, as there is no resulting displacement.

This foundational concept sets the stage for later discussions about energy, forces, and their interconnections in various physical contexts, making it essential for students to grasp early on.