How to generalize

The Transition Between Investigation and Explanation

May 3

Scientists have to decide how their results do and don’t apply to the phenomenon, making sense of differences such as scale and type of material. Engaging students with this form of uncertainty can help them rethink their investigation, considering what it did and didn’t tell them, and gaining a better understanding of the phenomenon as new aspects of it become important.

A closer look at uncertainty in the classroom

While other materials change state when children investigate heating them on a hot plate, the rock stays solid. They must decide whether they can claim that heat cannot change a rock. Uncertainty about how to generalize arises and supports children’s use of evidence and understanding of scale as:

The class observes a material that doesn’t change
Children make, disagree about, and qualify claims
The class uses a new resource to develop explanations

The class observes a material that doesn’t change

Rather than only observing materials that will change state (ice, egg, butter), children also make predictions about and observe a rock – which will not change state within the temperatures used in the investigation.

Children make, disagree about, and qualify claims

After they make and justify claims about some of the materials that did change, Lauren asks children whether they claim that heat changes the state of a rock.

Felisa: No

Serena: It was hot but the rock wasn’t melting. It stayed in its own shape. It didn’t start to break into pieces.

Devon: So it didn’t break or even break a little bit, but I think if you had more heat-like a whole bunch of heat for a really, really long time, I think it would start to break off.

Kenji: Lava is melted hot rock. It is kind of like a liquid rock at such a high temperature. It is super hot.

Maya: Yeah!

Yonas: Yeah, there is rocks in lava.

Lauren: Do you think because the temperature was so hot, this is how the rock was able to melt? (Yes) Do you agree with what Devon and Maya are proposing that if we had a longer time and we had much higher heat that the rock would melt and would become a liquid?

Kenji: No. Because it has to be something way more hot than the stove.

Devon: But what if it wasn’t an oven. Like if it wasn’t an oven it would melt. Like a lot lot hotter. A lot hotter would melt. We didn’t say it was the oven, we just said more heat.

Eve: Devon, can I clarify just one thing? … if you are going to make a claim here, does heat change the state of rocks? Would your claim be it doesn’t, or would your claim be ‘yes, it can with more heat’?

Lauren points out we now have two different claims, writes each on the chart paper, and says, “maybe we need more information of what other scientists have experienced with rocks.”

Lauren records both claims – that the rock doesn't change with heat and that it could with more heat – along with children's evidence on the class chart.

The class uses a new resource to develop explanations

Lauren introduces a video on volcanos and lava, asking children to use it to address their disagreement. They learn that lava is melted rock, ask about the temperature, and find out that it is 1000-2000 degrees Fahrenheit when it comes out of the volcano as melted rock.

Over the course of the unit, Lauren adds temperatures used to a thermometer. She now adds the new information about the temperature at which rock melts.

Instructional moves to support this form of uncertainty

Propose an outrageous claim and ask students to engage with it, e.g., “I’m going to claim that heat cannot change a rock because…”
Routinely ask students, “Does that make sense to you based on your experience? Do you think that would happen (outside the school; inside the cake?)”
Attune to hedging and qualifying language and probe students’ thinking when you hear “Maybe….” “kind of” “If/Only if ….” Attend to differences they think are consequential.
Provide resources that help students consider phenomena at larger and longer scales than those they can investigate.