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in the Mystery Box activity, getting students to ask questions to identify which object (by color, shape, and size) is inside the box.

Performance item: Give students a set of objects that vary along a given dimension (length, area, weight, or volume). Ask them to measure the dimension in question and make a data table that shows the values of each of the objects for that dimension.

Interpretation: These items call for students to construct simple but organized tables to represent their data in clear ways. An important aspect of their performance would be their ability to describe each object accurately and completely according to all the properties or dimensions in question and to have separate columns (or rows) for each property or dimension.

Paper and pencil item: Here are two empty balloons in balance. (Show picture or drawing of two uninflated balloons in balance, each hanging from the end of a rod that is suspended with a string tied to its midpoint.) Which of the following pictures shows what will happen when one balloon is filled with air? How do you know?

1. Picture shows the uninflated and inflated balloons are both still in balance.

2. Picture shows the inflated balloon is heavier (tips down).

3. Picture shows the inflated balloon is lighter (tips up).

4. There is no way to predict from the information given.

Interpretation: This item assesses whether students realize that air has weight and hence that adding air will make the balloon heavier and the rod tip down. If students understand this, they should select B and explain that air has weight, so it should make the rod go down. Common alternative ideas are that air is weightless (adding air will not change how things balance) or that air has negative weight (things rise when air is in them, so the side of the rod with the balloon will go up). Other items could be created, asking about the weight of a ball (or tire) as air is added or removed.

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