One of the most effective ways to teach something is to do a simulation—put the students “inside” the subject. I love doing this with systems of the body where the kids get to be actual body parts (muscles, blood cells, lungs etc.) and model how they work. We started our study of anatomy with bones and muscles, and did a simulation to show how they work together to make the body move.
Three kids worked in a group. One sat on the scooter (the bone we want to move). The other two were muscles, and were connected to the bone by ropes (tendons). Since muscles can only pull (or contract), not push, a muscle can only pull the bone one way. To get the bone back to where it started, you need another muscle on the other side to pull the other way.
The kids learned from the simulation how muscles are attached to bones with tendons to help you move, can only pull, and work in opposing pairs to move your body around. Educational and fun!