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The Use of Themes in Science
by Dr. Stearns W. Rogers

Most science educators agree that individuals can participate fully and most effectively in our society only if they are scientifically literate. A scientifically literate person is a person who can use the science they “learn” through their experiences in science classrooms and in life experiences to make useful and productive decisions. The American Association for the Advancement of Science’s Benchmarks for Science Literacy advocates the use of common themes as a powerful tool in the task of enabling individuals to achieve scientific literacy. The Benchmarks themes—systems, models, constancy and change, and scale—have been used to aid understanding of nature since people first began analyzing their world. The cycling of the seasons, day and night, the phases of the moon, simple and complex machines, and the interactions of organisms are but a few of the objects and phenomena that exhibit common themes.


A scientifically literate person should be able to identify the parts of a system and recognize how the parts work together as the system functions. Science experiences for primary students should help the learner understand that most things are made up of parts, that if parts are missing the system may not work, and that putting parts together enables the system to do things that the parts themselves can’t do. A flashlight that “lights” requires a casing, good cells, and a functional bulb. All three parts are required for the flashlight to work. Examples of systems that are routinely introduced in grades K–5 include the solar system, living systems, human body systems, the ecosystem, food chains, food webs, simple machines, and electrical systems. As students progress through their elementary school science experiences, they should appreciate and master the ideas that the parts in a system usually affect one another and that each part must be functional and in the right place if the system is to work. The flashlight works if the cells are placed in the flashlight in the proper manner and if the cells make contact with the bulb. Students who leave the fifth grade understanding and using these ideas realize that systems may include processes as well as things, that each part of the system has a specific function, and that systems are often composed of subsystems.


Physical models, mental models, computer models, and mathematical models are tools that help students explore, appreciate, and understand real-world phenomena. Models are designed to resemble or function like the objects and phenomena that they represent. In primary grade classrooms, learners can use toys as physical models of real-world counterparts. Students should understand that toys are different from real-world counterparts in size, details, and the way they work. Using toys allows students to compare objects. Toys also model some of the functions of the real-world objects. As students progress through the upper elementary grades, they should understand and appreciate that changes in their physical models may suggest how changes in real-world things may work.

Benchmarks states, "By the end of the fifth grade, students should know that geometric figures, number sequences, graphs, diagrams, sketches, number lines, maps, and stories can be used to represent objects, events, and processes in the real world, although such representations can never be exact in every detail". Computer programs and simulations can also be used to model real-world events.

Constancy and Change

Benchmarks states "Much of science and mathematics has to do with understanding how change occurs in nature and in social and technological systems, and much of technology has to do with creating and controlling change". Being able to identify those parts of a system that can or do remain constant and those parts of a system that can or do change is often essential in analyzing change.

In primary classrooms students should collect, observe, and classify objects that occur in their world. Kindergarten through second-grade students should understand that things in their environment change in some ways and stay the same in some ways. The sun rises in the morning and sets in the evening, but the time that the sun rises and sets changes.

K-2 students can observe and, in many cases, measure changes in color, size, weight, and movement. Oak tree leaves change colors as the seasons change, but their shape usually stays the same. Changes in the student’s height, weight, and running speed are easy to measure and are of interest to the student.

As students progress from grade 3 through grade 5, they should understand and be able to use the idea that certain features of things may remain constant while other features of the same things may change. A triangle may look different as it is rotated in space; likewise a caterpillar may look different as it is rotated in space.

Students leaving the fifth grade should understand that things may change in steady, repetitive, or irregular ways. Tables and graphs should be used by students to record the changes they observe.

Students encounter vast differences in magnitude in variables, such as temperature, velocity, size, distance, weight, volume, and force, in their environment. By the end of the second grade students should understand and appreciate that things in the world around them, have different sizes. Playing a game (which is greater and which is less?) is a simple way of comparing sizes, volumes, distances, weights, and speeds. This is a simple way to demonstrate ranges and limits. By the end of the fifth grade, students should understand that almost any object is limited as to how large or how small the object can be.

A discussion of length of cars, height of buildings, weight of trucks, volume of food containers and length of measuring tapes gives students some real-world examples.

The students should also realize that determining the largest and smallest possible values of something is often times as useful, as knowing the average value of the item.

Themes, like process skills, are not part of science content. They are, however, important tools that enable us to understand and use science content.


  1. Stremmel, A. J., and V. R. Fu. “Teaching in the zone of proximal development: Implications for responsive teaching practices.” Child and Youth Care Forum 22 (1993), pp. 337-350.
  2. Bredekamp, S., and T. Rosegrant, eds. Reaching potentials: Appropriate curriculum and assessment for young children. Vol. 1, p. 81. Washington, D.C.: NAEYC, 1992.
  3. Bredekamp, S., and T. Rosegrant, eds. Reaching potentials: Transforming early childhood curriculum and assessment. Vol. 2, p. 168. Washington, D.C.: NAEYC, 1995.
Dr. Stearns W. Rogers is Professor of Chemistry at McNeese State University, Lake Charles, Louisiana.
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