1. SCIENTIFIC EXPLANATION
Why Scientific Explanations?
Science education reform efforts call for students to develop
scientific processes and skills through inquiry (American
Side Note
Association for the Advancement of Science, 1993; National Found that having students
Research Council, 1996). One prominent inquiry practice in both engage in explanation changes
or refines their image of
the standards documents and research literature is the science as well as enhances
construction, analysis, and communication of scientific their understanding of the
nature of science (Bell & Linn,
explanations. We believe that explanation construction should be 2000). Third, onstructing
an important part of science class for three reasons. First, explanations can enhance the
students’ understandings of
research into scientists’ practices portrays a picture where the science content (Driver,
scientists construct arguments or explanations including weighing Newton & Osborne, 2000).
evidence, interpreting text, and evaluating claims (Driver,
Newton, & Osborne, 2000). Second, previous research in science education has found that having
students engage in explanation changes or refines their image of science as well as enhances their
understanding of the nature of science (Bell & Linn, 2000). Third, constructing explanations can
enhance the students’ understandings of the science content (Driver, Newton & Osborne, 2000). A deep
understanding of science content is characterized by the ability to explain phenomena (Barron et. al.
1998). Consequently, evaluating students’ explanations can also provide teachers with an opportunity
to assess students’ current understanding.
Although explanations are often cited as important for classroom science, they are frequently left out
of classroom practice (Kuhn, 1993; Newton, 1999). One of our goals in creating this unit was to make
students’ explanation construction an important part of the instructional sequence. Previous research
has found that making scientific thinking strategies, like explanation, explicit to students can facilitate
students’ use and understanding of these strategies (Herrenkohl, Palinscar, DeWater, & Kawasaki,
1999; Toth, Klahr& Chen, 2000). One of the ways we hope to help students with explanations is by
making the conventions (behind explanations and the reasons why explanations are important) clear to
students. We do this when we first introduce students to explanations (Lesson 6). We then continue to
support students’ writing of explanations through supports in both the activity sheets and student
reader. Furthermore, we provide suggestions to the teacher about difficulties that students might have
as well as ways to support students with the construction of explanations.
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2. What is a Scientific Explanation?
A scientific explanation is a written or oral response to a question that requires students to analyze
data and interpret that data with regard to scientific knowledge. Our explanation framework includes
three components: claim, evidence, and reasoning. While we break down explanations into these three
components for students, our ultimate goal is to help students to create a cohesive explanation in
which all three components are linked together. Yet we have found that first breaking explanations
down into the three components can ultimately help students create cohesive explanations. In the
following section, we describe the three components of a scientific explanation as well as provide an
example of one student’s explanation to illustrate the different components.
Student Example
Question: “Write a scientific explanation stating whether you think fat and soap are the same
substance or different substances.”
Student response: “Fat and soap are different substances. Hardness was different for fat and soap.
Also, fat dissolves in oil, soap does not dissolve in oil. The fat melts at 24° C and soap melts at way
above 100° C. Fat and soap are both white. Even though they are the same colors, they are different
substances because they have a lot of other different properties. Different substances have different
properties.”
Claim
The claim is a testable statement or conclusion that answers the original question. For instance, in the
student example above the claim is “Fat and soap are different substances.” The claim is the simplest
part of an explanation and often the part students’ find the easiest to include as well as to identify
when they are critiquing other peoples’ explanations. One of the purposes in focusing on scientific
explanations is to help students include more than a claim in their writing.
Evidence
The evidence is scientific data that supports the student’s claim. This data can come from an
investigation that students complete or from another source, such as observations, reading material,
archived data, or other sources of information. Depending on the claim being made, this data can be
qualitative or quantitative. In the student example above, the evidence comes from investigations the
student conducted, “Hardness was different for fat and soap. Also, fat dissolves in oil, soap does not
dissolve in oil. The fat melts at 24° C and soap melts at way above 100° C. Fat and soap are both
white.”
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3. The data needs to be both appropriate and sufficient to support the claim. When introducing evidence
to middle school students, we suggest discussing appropriate data in terms of whether the data
supports the claim. For this question, using the data that soap is used to wash clothes while fat is used
to cook is not appropriate data because students learn in the unit that properties are used to
determine whether two objects are the same or different substances. Consequently, it is also not
appropriate to include “volume” or “mass” as evidence, even though they are scientific data. This is
because volume and mass are not properties so they cannot be used to compare substances. A good
explanation only uses data that supports the claim in answer to the original question. In this example,
students need to use properties, like melting point or solubility, to support their claim.
Students should also consider whether or not they have sufficient data. When introducing this concept
to middle school students, we suggest discussing sufficient data in terms of whether they have enough
data. During the unit, students learn that using one property will not necessarily tell them if two
objects are different substances. For instance, two substances might be soluble in water. This is not
enough evidence to tell if the substances are the same or different. Instead, students need to include a
number of properties to support their claim.
When students are selecting their data to use as evidence, they should consider both whether it is
appropriate to support their claim and whether they have enough data to support their claim. We have
found that this can be difficult for students. While they realize that they should include data as
evidence, they are not necessarily sure which data to use or how much data to use.
Reasoning
Reasoning is a justification that shows why the data counts as evidence to support the claim and
includes appropriate scientific principles. The reasoning ties in the scientific background knowledge or
scientific theory that justifies making the claim and choosing the appropriate evidence. In the student
example above, the reasoning statement is “…they are different substances because have a lot of other
different properties. Different substances have different properties.” This statement tells why the
student used color, hardness, solubility and melting point as evidence (i.e. they are properties) and
includes the scientific theory that different substances have different properties to justify using the
evidence to support the claim.
We have found that students have a difficult time including the entire reasoning component in
scientific explanations. Often students simply make a general link between the claim and evidence. For
example, students may say, “Since fat and soap have different densities and melting points, they are
different substances.” In this example, the reasoning supporting the link between claim and evidence
is not explicit. You want to help students learn to include the scientific background knowledge that
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4. allowed them to make that connection between claim and evidence. They should include the scientific
principles that different substances have different properties.
How To Support Students’ Construction
of Scientific Explanations
Many middle school children will find constructing scientific explanations as difficult. It is not an
inquiry skill that they can learn quickly. Students need support in terms of when, how, and why to use
the claim/evidence/reasoning framework. We suggest using a number of techniques during the unit to
help students with this new inquiry process. Some of these techniques are embedded in the curriculum
materials. We also encourage you to use them during classroom discussions in order to make
explanation an important component of everyday classroom practice.
1. Make the framework explicit. You want to help students understand the three components of
explanations. They should understand what these three components are as well as the
definitions of the three components.
2. Model the construction of explanations. After introducing explanations, you want to model
how to construct explanations through your own talking and writing. When it is appropriate,
provide students with examples of explanations. Furthermore, identify for students where the
claim, evidence, and reasoning were in your own example.
3. Encourage students to use explanations in their responses. During class discussions, if a
student makes a claim ask them to provide an explanation for that claim. Encourage students
to provide evidence and reasoning to support their claims.
4. Have students critique explanations. When students write explanations in class, you may want
to have them trade their explanations with a neighbor and critique each other’s explanations.
Focus students’ attention on discussing both the strengths and weaknesses of their partners’
explanations and offering concrete suggestions for improvement. Instead, you may want to
show students an overhead of a generic student’s response and as a class critique the
explanation. Or you may want to provide students with an example of a scientific explanation
from a newspaper, magazine or website. Then you could have students critique the explanation
in terms of the claim, evidence, and reasoning.
5. Provide students with feedback. When students construct explanations, comment on their
explanation as a whole as well as the quality of the individual components. You may want to
coach them on how to improve their explanations by asking them leading questions or providing
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5. them with examples. For example, you may want to ask students what the reasoning was in
their explanation and how they might improve their reasoning.
While supporting students’ construction of scientific explanations can be a time-consuming process,
there are numerous benefits. Helping students understand and be able to construct explanations can
result in a greater understanding of science content and science as an inquiry process.
References
American Association for the Advancement of Science. (1993). Benchmarks for science literacy. New York: Oxford
University Press.
Barron, B., Schwartz, D., Vye, N., Moore, A., Petrosino, A., Zech, L., Bransford, J., & The Cognition and
Technology Group at Vanderbilt. (1998). Doing with understanding: lessons from research on problem- and
project-based learning. The Journal of the Learning Sciences. 7 (3&4), 271-311.
Bell, P., & Linn, M. (2000). Scientific arguments as learning artifacts: Designing for learning from the web with KIE.
International Journal of Science Education. 22 (8), 797-817.
Driver, R., Newton, P. & Osborne, J. (2000). Establishing the norms of scientific argumentation in classrooms.
Science Education. 84 (3), 287-312.
Herrenkohl, L. R., Palinscar, A. S., DeWater, L. S., & Kawasaki, K. (1999). Developing Scientific Communities in
Classrooms: A Sociocognitive Approach. The Journal of the Learning Sciences. 8(3&4), 451-493.
Kuhn, D. (1993) Science as argument: Implications for teaching and learning scientific thinking. Science Education,
77, 319-338.
National Research Council. (1996). National science education standards. Washington, DC: National Academy
Press.
Newton, Paul. (1999). The place of argumentation in the pedagogy of school science. International Journal of
Science Education, 21 (5), 553-576
Toth, E. E., Klahr, D., Chen, Z. (2000). "Bridging research and practice: A cognitively based classroom intervention
for teaching experimentation skills to elementary school children." Cognition & Instruction 18(4): 423-4
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6. Samples of student work – explanation
Write a scientific explanation stating whether these are the same or different substances.
Properties
Color Hardness Solubility Melting Point Density
Off white
Water – No
Soft
or
47° C 0.92 g/cm3
Fat Squishy
Slightly
Oil – Yes
yellow
Water – Yes
Higher than
Milky white Hard 0.84 g/cm3
100° C
Soap
Oil – No
Quality Example:
Fat and soap are different substances (correct claim). Fat is off white and ivory is milky white. Fat is soft
squishy and soap is hard. Fat is soluble in oil, but soap is not soluble in oil. Soap is soluble in water, but
fat is not. Fat has a melting point of 47° C and soap has a melting point above 100° C. Fat has a density
of 0.92 g/cm3 and soap has a density of 0.84 g/cm3 (correct evidence). These are all properties.
Because fat and soap have different properties, I know they are different substances. Different
substances always have different properties (correct reasoning).
Examine the following data table:
Density Color Mass Melting Point
3
Liquid 1 0.93 g/cm no color 38 g -98 °C
Liquid 2 0.79 g/cm3 no color 38 g 26 °C
Liquid 3 13.6 g/cm3 silver 21 g -39 °C
Liquid 4 0.93 g/cm3 no color 16 g -98 °C
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7. Write a scientific explanation that states whether any of the liquids are the same substance.
Example 1:
Example 2:
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