Formative Assessment

Can students annotate their change over time graphs to explain changes in their mini-lakes?

Look at students’ annotated graphs (Weight of mini-lake over time) and listen for evidence as they discuss the changes in the mini–lake weights.

Use these criteria to interpret students’ annotations and explanations:

• The shape of the data: A horizontal (flat) line represents no change in weight, a sloped line represents an increase or decrease in weight.
• When the mini–lake is a closed system (the cover is on), there is little or no change in weight (horizontal line).
• When salt is added, the weight increases immediately (line rises vertically).
• When the cover is removed, the weight decreases over time (downward sloping line) until there was no more water left to evaporate (horizontal line).
• Fluctuations in weight (+/- 1 gram) can be attributed to the inaccuracy of the scale.
• The weight of the water put in the mini-lake initially (in data table) is the amount of weight lost through evaporation.

As a next step, ask students if they can think of one or two ways the story of their mini-lake might be the same as the story behind the Ships in a Field.