Skip to main content

Middle School    |    Formative Assessment Probe

Iron Bar

By Page Keeley

Assessment Physical Science Middle School

Sensemaking Checklist

This is the new updated edition of the first book in the bestselling Uncovering Student Ideas in Science series. Like the first edition of volume 1, this book helps pinpoint what your students know (or think they know) so you can monitor their learning and adjust your teaching accordingly. Loaded with classroom-friendly features you can use immediately, the book includes 25 “probes”—brief, easily administered formative assessments designed to understand your students’ thinking about 60 core science concepts.

Iron Bar

Access this probe as a Google form: English

Download this probe as an editable PDF: English



The purpose of this assessment probe is to elicit students’ ideas about atoms. The probe is specifically designed to determine whether students can use the idea of atoms to explain why a metal expands when heated. Furthermore, older students’ explanations may reveal whether these students use the kinetic molecular theory to explain how heating causes the atoms to vibrate more, thus pushing the atoms apart.

Type of Probe

More A-More B

Related Concepts

atoms, thermal expansion


The best answer is C: The space between each atom increased. Thermal expansion of metals involves the tendency of a metal to increase in volume in response to an increase in temperature. As a metal object is heated, its atoms vibrate in place more vigorously and, as a result, increase the separation between individual atoms. This slight increase in the empty space between atoms results in a cumulative change in the measurable volume of the object. The object expands. When the object expands, no new atoms are added. Although the length or width of the metal object may increase, the size of the atoms it is made of stays the same. It is the space between the atoms that increases and contributes to an increase in volume. As the atoms of a solid gain energy, they vibrate more in place. Unlike a gas, which is free to move about, the metal atoms maintain their general positions.

Curricular and Instructional Considerations

Elementary Students

In the elementary grades, students observe macroscopic properties of matter, including changes caused by heating. Their observations focus on objects and materials. Explanations of phenomena that use the idea of atoms should wait until middle school or when students are ready to use this abstract idea.

Middle School Students

In the middle grades, students begin to use atomic and molecular ideas to explain phenomena. They begin to relate the expansion and contraction associated with the heating and cooling of substances to the position and motion of particles. However, students at this level may still confuse the properties of the material or substance with the properties of the atoms or molecules of which they are made.

High School Students

Students at the high school level should be able to use ideas about atomic/molecular motion to explain phenomena from a microscopic view. They should be able to distinguish between the observable properties of a substance and the properties of the atoms making up the substance. However, many students at this stage will attribute expansion of the solid material to an increase in the amount of matter and/or an increase in the size of the atoms rather than to the space between them.

Administering the Probe

Make sure students understand the phenomenon. Consider providing real-life examples of similar phenomena, such as the space between the metal joints on a bridge expanding in the summer or a metal door that sometimes scrapes against the floor on a hot summer day. The ball and ring apparatus sold in science supply stores can also be used by demonstrating how the metal ball can no longer pass through the ring when it has been heated.

Related Disciplinary Core Ideas (NRC 2012; NGSS Lead States 2013)

6–8 PS3.A: Definitions of Energy

  • Temperature is a measure of the average kinetic energy of particles of matter. The relationship between the temperature and the total energy of a system depends on the types, states, and amounts of matter present.
Related Ideas in National Science Education Standards (NRC 1996)

K–4 Properties of Objects and Materials

  • Objects have many observable properties, including size, weight, shape, color, temperature, and the ability to react with other substances.
  • Objects are made of one or more materials, such as paper, wood, or metal. Objects can be described by the properties of the materials from which they are made.

5–8 Transfer of Energy

  • Energy is transferred in many ways.

9–12 Conservation of Energy and the Increase in Disorder

  • Heat consists of random motion and the vibrations of atoms, molecules, and ions. The higher the temperature, the greater the atomic or molecular motion.*

*Indicates a strong match between the ideas elicited by the probe and a national standard’s learning goal.

Related Ideas in Benchmarks for Science Literacy (AAAS 1993 and 2008)

Note: Benchmarks revised in 2008 are indicated by (R). New benchmarks added in 2008 are indicated by (N).

K–2 Structure of Matter

  • Objects can be described in terms of their properties. Some properties, such as hardness and flexibility, depend on what material the object is made of, and some properties, such as size and shape, do not. (R)
  • Things can be done to materials to change some of their properties, but not all materials respond the same way to what is done to them.

3–5 Structure of Matter

  • Heating and cooling can cause changes in the properties of materials, but not all materials respond the same way to being heated and cooled. (R)
  • Materials may be composed of parts that are too small to be seen without magnification.
  • All materials have certain physical properties, such as strength, hardness, flexibility, durability, resistance to water and fire, and ease of conducting heat. (N)

6–8 Structure of Matter

  • All matter is made up of atoms that are far too small to be seen directly through a microscope.
  • Atoms and molecules are perpetually in motion. Increased temperature means greater average energy of motion, so most substances expand when heated. In solids, the atoms are closely locked in position and can only vibrate.*

6–8 Energy Transformations

  • Thermal energy is transferred through a material by the collision of atoms within the material. Over time, the thermal energy tends to spread out through a material and from one material to another if they are in contact. (R)

9–12 Structure of Matter

  • An enormous variety of biological, chemical, and physical phenomena can be explained by changes in the arrangement and motion of atoms and molecules.*

*Indicates a strong match between the ideas elicited by the probe and a national standard’s learning goal.

Related Research

  • Students of all ages show a wide range of beliefs about the nature and behavior of particles. For example, they attribute macroscopic properties to particles; do not accept the idea there is empty space between particles; and have difficulty accepting the intrinsic motion of solids, liquids, and gases (AAAS 1993).
  • Children frequently consider atoms of a solid to have all or most of the macroproperties they associate with the solid (Driver et al. 1994).
  • Some older students (ages 11–16) who had learned about the kinetic molecular theory of matter attempted to explain conductivity phenomena in terms of particulate ideas. However, these ideas were not used spontaneously by most of the students interviewed. When they did use particle ideas, they had a tendency to attribute expanding (getting bigger) to the properties of the atoms (Driver et al. 1994).
  • Children’s naive view of particulate matter is based on a “seeing is believing” principle in which they tend to use sensory reasoning. Being able to accommodate a scientific particle model involves overcoming cognitive difficulties of both a conceptual and perceptive nature (Kind 2004).

Related NSTA Resources

Association for the Advancement of Science (AAAS). 2001. Atlas of science literacy. Vol. 1. (See “Atoms and Molecules” map, pp. 54–55.) Washington, DC: AAAS.

Michaels, S., A. Shouse, and H. Schweingruber. 2008. Ready, set, science! Putting research to work in K–8 science classrooms. Washington, DC: National Academies Press.

Robertson, W. 2007. Chemistry basics: Stop faking it! Finally understanding science so you can teach it. Arlington, VA: NSTA Press.

Suggestions for Instruction and Assessment

  • Demonstrate the phenomenon with the ball and ring apparatus sold by most science supply companies. Before heating, the ball easily passes through the ring. After the ball is heated, it expands and will no longer pass through the ring when warm. Ask students to describe what happened to the ball itself. Then ask students to describe what happened to the atoms that make up the ball. Ask them to describe the difference between the phenomenon at the substance level versus the atomic level.
  • Encourage students to draw “atomic pictures” of what they think is happening to the atoms as the metal is heated.
  • Have students generate a list of other things that expand when heated and describe what is happening to the atoms or molecules.
  • Ask students what happens to the metal when it cools down. Have them explain what happens at both the substance and atomic level.
  • The PRISMS (Phenomena and Representations for Instruction of Science in Middle Schools) website at http://prisms. has a collection of web-based phenomena and representations aligned to the Benchmarks for Science Literacy (AAAS 1993) and Curriculum Topic Study Guides (Keeley 2005) that can be used to help students understand why metals expand when heated.

American Association for the Advancement of Science (AAAS). 1993. Benchmarks for science literacy. New York: Oxford University Press.

American Association for the Advancement of Science (AAAS). 2008. Benchmarks for science literacy online. bsl/online

Driver, R., A. Squires, P. Rushworth, and V. Wood- Robinson. 1994. Making sense of secondary science: Research into children’s ideas. London: RoutledgeFalmer.

Keeley, P. 2005. Science curriculum topic study: Bridging the gap between standards and practice. Thousand Oaks, CA: Corwin Press.

Kind, V. 2004. Beyond appearances: Students’ misconceptions about basic chemical ideas. 2nd ed. Durham, England: Durham University School of Education. Also available at education/teachers/learnnet/miscon.htm

National Research Council (NRC). 1996. National science education standards. Washington, DC: National Academy Press.

Asset 2