An important step in constructing scientific explanations is generating evidence-based claims. When students are required to provide evidence in support of what they believe, they are likely to reach a deeper understanding of the content. An important part of scientific understanding is the ability to evaluate claims based on the quality of evidence used to support them (National Research Council, 2000). In addition to providing relevant evidence, it is important that students understand the importance of providing a sufficient amount of evidence to strengthen the validity of their claims (Sandoval, 2001).
Currently, new science standards are being prepared under the working title “Next Generation Science Standards.” In preparation for these standards, the National Research Council has written a guiding document, based on the most current research in science education. The Framework for K-12 Science Education places a strong emphasis on the importance of evidence-based claims.
Although the practices used to develop scientific theories (as well as the form that those theories take) differ from one domain of science to another, all sciences share certain common features at the core of their inquiry-based and problem-solving approaches. Chief among these features is a commitment to data and evidence as the foundation for developing claims. (National Research Council, 2012)
Much research has been done in recent years to determine methods for effectively supporting students in the process of writing scientific explanations. Results from this research have indicated that students form deeper understandings when new concepts are taught via scaffolding, that is, when teachers provide more support early and then gradually allow the student to perform independently (Mcneill, Lizotte, & Krajcik, 2000).
When introducing students to the process of constructing scientific explanations, I have found it effective to break the process into separate lessons. This method helps to ensure that students grasp the fundamentals and allows teachers to better detect misconceptions in regards to terminology. Therefore, I have made it a priority to establish clear working definitions of the terms involved (i.e. claim, evidence, reasoning) before engaging in application of the process.
There are several ways teachers can support students as they introduce the process of making evidence-based claims. First, establish clear definitions for the terms “claim” and “evidence.” Second, provide the class with examples of claims and related evidence. Next, model the process of evaluating the claims based on the evidence. Finally, guide the students as they construct their own claims based on teacher provided data.
During the introductory period, I have found it useful to provide the students with clear, objective, and quantitative data to use as evidence. In my experience, it is easier for the students to identify trends and relationships on which to base their claims when the data are quantitative in nature. There are many governmental websites that maintain statistical databases on a wide range of topics. For example, the Data and Statistics page at USA.gov provides links to the data found on various governmental websites. Data from these sites can be freely downloaded and used in the classroom.
The following activity was used to introduce 10th grade General Biology and Advanced Placement (AP) Biology students to the process of writing evidence-based claims. The activity can be scaled to various academic levels through extended discussion.
The following is a discussion outline for introducing important concepts and terminology associated with the process of constructing evidence-based claims. Open-ended question are used to generate discussion. Bullet points are provided as possible talking points.
How do we gather information about the world around us?
- First hand experiences
- What other people tell us
What conclusions can we draw from observations?
- A carpenter, a school teacher, and scientist were traveling by train through Scotland when they saw a black sheep through the window of the train.
- “Aha,” said the carpenter with a smile. “I see that Scottish sheep are black.”
- “Hmm,” said the school teacher. “You mean that some Scottish sheep are black.”
- “No,” said the scientist glumly. “All we know is that there is at least one sheep in Scotland, and that at least one side of that one sheep is black.”
What do observations and experimentation provide us?
What can one do with data?
- Draw conclusions
- Make predictions
What is a claim?
- A statement of something as a fact; an assertion of truth. (TheFreeDictionary.com)
Consider the Following Claims
In the United States…
- More than twice as many males die in motor vehicle crashes than females.
- More fatal motor vehicle crashes occur during the night time.
- More fatal motor vehicle crashes occur when it’s raining than when it’s snowing or sleeting.
- A majority of fatal motor vehicle crashes occur when the weather is “normal” outside.
- Fewer older people die in motor vehicle crashes than younger people.
After reading the claims with the class, ask students to list the claims they find the most or least believable. Then ask the responding students to explain why they believe or disbelieve a particular claim. The explanations vary, but many students base their assumptions on what they have heard from friends and relatives or seen in the media.
The claims listed above are related to real data from the Fatality Analysis Reporting System (FARS) of the National Highway Traffic Safety Administration. Once students have stated and discussed their assumptions, you can display the FARS data and ask the class to determine if the claims are supported by the data.
FARS Data: use the tabs below to sort through graphs and tables created from the 2010 FARS Data.
Depending on the time available, I like to have a short conversation about how sometimes many people will believe a claim even though there is a large volume of research that rejects the claim. As an illustration, I have students vote, by raising their hands, on two opposing claims. The first claim is that human blood is blue in our veins and turns red when it leaves the body and encounters oxygen. The second claim is that human blood is always red, even inside our bodies. Surprisingly, I find the vote is usually split 50/50. I then tell the students that a major function of the blood is to carry oxygen throughout the body via the red blood cells and the blood is rarely without oxygen. Furthermore, I explain that even deoxygenated blood is still red, albeit dark red.
I then present the following question and possible responses.
Why do people believe claims?
- They trust the source.
- It sounds believable.
- They hear the claim made from various sources.
- The claim is supported by experimental data (evidence).
I ask the students to tell me which reason for believing a claim they find the most trustworthy. Many students will begin by listing “various sources” as the best reason to believe a claim. However, the class will usually settle on “experimental data” as the number one choice.
Students Write Claims
At this point, the stage is set for the students to begin writing their own claims. To facilitate this process, provide the students with a large data set from a reliable, preferably peer-reviewed, source. Large amounts of quantitative data can be found on various government websites. The Vital Statistics Reports from the Center for Disease Control (CDC) are a good example. I recently choose the document Deaths: Leading Causes for 2008 to use with my classes. These reports provide pages of good (albeit morbid) data tables listing the leading causes of deaths occurring in the United States. The data is broken down by age, sex, and race and offers comparisons across demographics.
For my classes, I print pages 17-23 of the document Deaths: Leading Causes for 2008. These pages feature data for the leading causes of death across the demographics of age and gender. I ask the students to review the data in small groups of 2-3. Each student is given a blank T-chart and asked to make five claims and provide supporting evidence for each claim.
In the beginning of this exercise, I give my students the following words of advice.
- The claims can indicate difference in and between demographic categories.
- Then number of deaths in each demographic group varies. It is therefore important to use percentages as opposed to numbers of individuals.
- Claims should be clearly supported by the data. Indicating differences between demographics is sufficient. Do not offer suggestions as to why the differences exist.
Once the students have had time to analyze the data and record their claims, I provide them with a question that can be answered through a review of the data : “How does a person’s age affect the likelihood they will die because of an accident?”
In order to make a claim that addresses this question, students are required to compare the percentage of individuals dying from accidents across each age range. To support my students in this process, I ask them to create a line graph to visualize the relationship between age group and accidental death rate. I’ve created a pre-formatted graph to save time in the classroom.
After students have a chance to create their line graphs, they must make a claim that adequately explains the relationship between age and accidental death rate as represented in the provided data set, and they must list data to support their claim.
To end the activity, I ask students to state their claims to the class. I type the student claims as they are spoken and display them to the class via a projector. The following is a table of selected student responses from a General Biology class and an Advanced Placement (AP) Biology class.
Tips and Suggestions:
- As students discover differences between age and gender groups, they may be tempted to offer explanations for these differences as a part of their claim (as indicated in some of the student responses above). Encourage students to exclude any assumptions that are not directly supported by the data. In order to highlight this point, I discuss the leading causes of death in males versus females. I point out that death from unintentional injuries is more common in males. This often leads to statements about male behavior that are based on popular culture; for example, stereotypes suggest males are “risk takers” or “like to show off.” I point out that these claims would need to be supported by additional evidence that clearly demonstrate an increase in these behaviors among men.
- As demonstrated in the above responses, students might use unclear pronouns in their claims. Consider the previous student statement: “After the age of 25 the likelihood they will die from an accident falls.” A better statement is, “After the age of 25, the likelihood a person will die from an accident falls.” The unclear pronoun “they” was replaced with the specific noun, “person.”
- Having the students critique each other’s claims is a beneficial process. This allows students to participate in determining which characteristics the “best” claims share. The group discussion allows the class to form a model of the way a claim should look through consensus as opposed to direct instruction from the teacher.
Student HandoutsMaking a Claim Based on Data (T-Chart) Comparing Age and Accidental Death Line Graph
McNeill, K. L. Lizotte, D.J., Krajcik, J., & Marx, R.W. (2000). Supporting Students’ Construction of Scientific Explanations By Fading Scaffolds in Instructional Materials. The Journal of the Learning Sciences, 15(2), 153-191
National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas. Washington, DC: The National Academies Press, 2012.
National Research Council. Inquiry and the National Science Education Standards: A Guide for Teaching and Learning. Washington, DC: The National Academies Press, 2000.
Sandoval, W. A. Students’ Uses of Data as Evidence in Scientific Explanations. Paper presented at the Annual Meeting of the American Educational Research Assn. Seattle, WA, April 10-14, 2001.
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