Evaporation is a challenging idea for students moving from concrete thinking to abstract concepts. (Jon was instrumental in all of my experiments by loaning me the actual materials. It is easier to imagine yourself as a scientist when you have actual beakers, cool thermometers, etc.)
My #1 backward design element was trying to show evaporation--other parts of the water cycle have been observed by the students in their lives. (Well, condensation can be exhibited in an easy experiment and/or brought to their attention by observing our weather, watching clouds form.) The second was to mathematical and scientific concepts as well as incorporate temperatures, graph, degrees, thermometer, evaporation, evaporating, beakers, milliliters, and evaporate into our daily language.
This experiment had the added factor of hot (102 degrees) and cold (64 degrees) water at the start of the experiment. The young scientists used thermometers to measure the temperature. We marked on the beakers to record the amount in milliliters and the temperature. One girl was in charge of the "hot" beaker and the other recorded information about the "cold" one on graphs.
The water was evaporating very much, a discussion ensued, and it was decided that maybe we should move it to a window. Jackie was kind enough to let us use her sill. The experiment continues, we usually check the amounts on Wednesdays. Although they are still interested the impact wasn't what I had hoped for. My lesson is that in using small necked beakers, there is less surface exposed, therefore slower evaporation. Next year, I will use wide mouthed beakers to expedite the evaporation. I will most likely also use a warmer room.