Pressing for evidence-based explanations

Why do we use these particular practices?

This final set of practices will help students construct a final, evidence-based explanatory model for an anchoring event. The goals of this practice are:

  1. Engage all students in authentic disciplinary discourse around using evidence to support explanations.
  2. Hold students accountable for using multiple sources of information to construct final explanatory models for the anchoring event (this accountability of course must be supported by scaffolding and guidance from you).
  3. Support students in using evidence to support different aspects of their explanatory models.

We want to note here that this page does not describe the practices in depth—that is done in the primer document (see below).

Some important links to learn more about this set of practices:

Orientation videos that show this set of practices in action
Pressing for Explanations—the primer for learning about it
Pressing for Explanations—the tool for designing your own lessons

Brief intro about what the practices look like
This sequence of events happens with about two days left in a unit of instruction. Some parts of this practice, especially the talk about evidence, should certainly be used at other times during the unit when you are trying to get students to support claims they are making. The reason to leave a couple of days open after these practices, is so that students can then apply their explanatory models to events or processes that have not been the target of study so far (to understand how explanations can be generalizable) or to use the model to design a further investigations of interest to them, or to use the model to design a solution to a problem.

Zozone summary tableIn this practice the teacher asks students to be prepared to defend one key aspect of their explanatory model by using relevant evidence from a public record such as a summary table (see our Tools page). An example of a summary table is pictured to the left, recorded by a group of high school high school juniors studying the biological effects of ozone depletion.

This part of an explanation is called a claim (see our How do I? page). What is a claim? A claim is a statement about some event, process, or relationship in the natural world that you believe to be true. A claim, however, is not simply a statement about trends in data. You can think of a claim as a small part of a larger explanation. For students just beginning to use evidence, it is easier to focus on using evidence to support a specific claim rather than supporting an entire explanation (which can be composed of several integrated claims).

This part of the conversation starts with you saying something like: “I’d like you to select one part of your current explanation and describe evidence from one or more activities that supports that part of your explanation.” You should provide examples of what counts as a claim, what counts as evidence, and how you can support a claim with that evidence.

Following the first part of this practice, perhaps the following day, teachers would re-assemble the class and have groups of students compare claims with one another. These groups could defend one particular part of the explanation (their claim) to the class, cite the evidence used, and the reasoning they used to link the evidence with the claim (this is another instance in which sentence frames or other language support is effective). The teacher could select groups who have contrasting explanations to present publicly and ask the entire class to comment on the use of evidence and explanatory coherence. Questions here might be “What evidence appears to be convincing and why?”, “What gaps do we still have in our models/explanations?”, or “What is another way to interpret that evidence?”

In the second practice, drawing final ideas together in models and explanations, you are pressing students for a final explanatory model (drawn) and a gapless explanation (written). The model depicts, in words and drawings, a chain of reasoning linking observations and information from a variety of sources (first-hand data, second-hand data, information resources, known facts, concepts, laws, etc.) with theoretical (unobservable) events, structures, or processes. We emphasize—the model should show how the unobservable (the causes) and the observable (the effects) are linked. The fourth grade model below is of a flashlight left on over a period of days. This “before and after” model shows the observable (light, filament, batteries, etc.) and the unobservable (charge, electrons, energy transformations, etc.).


The teacher asks students in small groups to finalize their models (see the How do I? page), incorporating all relevant ideas and forms of evidence they have encountered during the unit. Even though the teacher and students have revised the explanatory models perhaps once during the unit, creating the final version would be difficult without special scaffolding and tools. Scaffolding moves might include:

• guides for what to include in an explanation (the use of specific science language, reminders to describe what is not observable)
• providing a model template for drawing into, and a designated space for students to write their explanations
• dividing a phenomenon and its explanation into “before, during and after”
• special tools should include student-created explanation checklists and a table that summarizes ideas and different type of evidence assembled across the unit (summary table).

As a result of all this thinking made visible the teacher has a good sense of what students understand. You have three good options at the end of the this practice—1) re-teach important ideas, 2) have students apply their models to a related phenomenon, or 3) conduct a more formal assessment of students’ understandings.

Remember, the video cases we have on this site are your best resources for seeing these practices come alive.


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