Observe rain and puddles, and understand that puddles dry up as water evaporates.
After it rains, puddles form on the ground. A few days later, they disappear!
Where does the water go? Watch and find out.
Mastery looks like: They can say that puddles shrink over time because the water rises into the air, and can name that word as evaporation.
Common stumbles: Thinking the water just disappears with no explanation is a fine starting point; the word evaporation can come later without pressure.