We used:
A clear cup, filled halfway with water
Shaving cream
Food coloring
The second graders used the shaving cream as a cloud on top of the water. The food coloring was used to create precipitation. The students had to come up with a hypothesis of how many drops it would take to cause the cloud to "rain". Then the second graders dropped food coloring onto the "cloud" and counted the drops.We then recorded our conclusions.