If you have two solid that have identical bases and height but one is a prism and one is a pyramid, students will often look at the two shapes and say that the pyramid will fit in the prism exactly twice.  Most students don't even think it could be three times. 

I have filled a square prism and square pyramid with water and the students are shocked that the pyramid fits in three times.  They can't figure out how that can work.

With this product you can show the students how the three pyramids fit into the square prism.  After students have seen this model, they never forget that the pyramid fits in the prism three times. 

Build-a-Model-Volume-of-a-Square-Prism-and-Volume-of-a-Square-Pyramid