They predicted whether the objects would sink or float, shared their predictions and rationale, tested their predictions, recorded the results, and wrote reports that they shared with the class.

The students were assigned rotating procedural roles, such as reporter, scribe, and poster designer. Working in small groups, they moved through a series of stations in which they were asked to order a set of objects, first by mass and then by volume, make predictions about sinking or floating, test their predictions, record the results, and prepare a report for the class. The objects used in the different stations were large and small cylinders, large and small cubes, and a set of spheres made of wood, Lucite, recycled plastic, and aluminum. A different subset of these items was used at each different station.

Following this period of exploration, predicting, and theorizing, the students were introduced to the dots-and-boxes model of mass, volume, and density. They worked on computers to explore and then apply a dots-and-boxes model of density to several different objects, some real and some imagined. They then revisited their earlier work, using the dots-and-boxes model, to explain their sinking and floating results with real objects. Finally, they applied the model (on and off the computer) in exploring thermal expansion—why it is that heated alcohol takes up more space but weighs the same and has decreased density. They also explored why certain objects sank in hot water but floated in cold water.

At the beginning of the investigation, Mr. Wilson decided to try something new—assigning roles for student audience members whenever a student group presented its findings. He hoped that this would help promote productive discussion and participation during student reports. This presentation time often had become more of a conversation between the presenting group members and Mr. Wilson, rather than involving the whole class as intended.

The students in the audience were assigned, on a rotating basis, one of three audience roles: checking predictions and theories, checking summaries of results, and assessing the relationship among predictions, theories, and results. These three roles were designed to help give guidance to the students as they explored, through talk, three important intellectual practices in science: predicting and theorizing, summarizing results, and relating predictions and theories to results (sometimes referred to as coordinating theory and evidence).







Checking predictions and theories

Predicting and theorizing


Checking summaries of results

Summarizing results


Assessing the relation between predictions, theories, and results

Relating predictions and theories to results

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