Essential Science for Teachers: Life Science
Classifying Living Things Children’s Ideas about Classifying Living Things
Below are common ideas children in grades K-6 have about this topic, compiled from research on children’s ideas about science (see the Session 2 Children’s Ideas Bibliography). For each idea, consider why a child would be likely to believe this and what evidence might refute it.
1. Animals are large, furry, four-legged land mammals.
Children often start with this narrow definition of the concept “animal” because of the vertebrate examples that are most familiar to them: pets and zoo specimens. Animals also include birds, snakes, frogs, fish, insects, snails, worms, starfish, jellyfish, etc.
2. Fish, snails, whales, and robins are not subsets of “animal” but parallel categories.
If children hold a narrow definition of the concept “animal” (i.e., large, furry, and four-legged), then it is reasonable that life forms that don’t fit their definition are considered to be parallel categories, even though they are animals. Using scientific criteria–animals are multicellular, their cells have a nucleus, their cells don’t have cell walls, and they must ingest food–their definition of animal can be broadened.
3. People are not animals.
The idea that people aren’t animals is likely to arise because children have previously applied the term to animals other than human beings, such as pets and zoo specimens. Humans do fit the scientific definition of an animal: they are multicellular, their cells have a nucleus, their cells lack cell walls, and they must ingest food.
4. Plants are small green things.
This is a narrow definition of the concept “plant” that may arise because children have more direct experience with plants of this nature, such as household and garden plants. Tall trees, bushy shrubs, and woody vines all share the same defining features of small, green plants: they are multicellular, their cells have a nucleus, their cells have cell walls, and they make their own food.
5. Seeds, fruits, vegetables, and flowers are not plants.
Children may not consider parts of a plant to fit the definition of a plant. However, the characteristics that classify something as a plant apply equally to the whole and its parts. Parts, attached or detached, aren’t classified into distinct groups.
6. When children use words like “insect,” “fish,” “amphibian,” and “moss,” they are thinking of more extensive groups than those defined scientifically.
Before children learn the scientific definitions for different groups of organisms, the definitions may be more loosely applied. All things that look like insects are insects, for example, or all things that swim in water are fish. Once children are introduced to more precise scientific definitions, they can use them to determine examples from non-examples.
7. Very young children do not classify groups systematically and may use different criteria for every member of a group.
Children may recognize that a group of organisms are all fish, for example, but they may place one individual in the group because it swims in water, another because it has fins, another because it has gills, and so on. As they are encouraged to look at one characteristic only and “test” each object for the presence of this characteristic, they can begin to learn to classify systematically.
8. Classification categories are thought of as separate “bins,” not as subsets of other categories.
The classification schemes with which most children are familiar involve “exclusive” categories, meaning that groups do not share members. Biological classification is built around hierarchical classification, in which one larger group includes smaller groups, with each smaller group including smaller groups, and so on. The criteria used to classify something into a larger group apply to all of the groups that it contains. For example, all animals ingest food. Fish, birds, and mammals are different groups of animals, but as animals, they all ingest food. Birds have feathers. Sparrows and hawks are different groups of birds, but as birds, they all have feathers. The criteria used to classify into groups on the same level (e.g., different vertebrate groups or different types of birds) is when distinguishing features come into play. Children may benefit from direct instruction that contrasts exclusive classification with hierarchical classification.
Children's Ideas Bibliography
The Children’s Ideas listed in this section of the Web site were compiled from the following research:
- Barman, C., et al. (1999). Assessing students’ ideas about animals. Science and Children 37(1): 44-49.
- Barman, C., et. al. (2000). Students’ ideas about animals: results for a national study. Science and Children, 38(1), 42-47.
- Braund, M. (1991). Children’s ideas in classifying animals. Journal of Biological Education, 25(2), 103-110.
- Carey, S. (1985). Conceptual change in childhood. Cambridge, MA: The MIT Press
- Driver, et al. (1992). Life and living processes. Leeds National Curriculum Support Project, Part 2. Leeds City Council and the University of Leeds, UK.
- Stavy, R. & Wax, N. (1989). Children’s conceptions of plants as living things. Human Development, 32, 88-94.
- Stovall, G. & Nesbit, C. (2003). Let’s try action research! Science and Children 40(6): 44-47.
Session 1 What Is Life?
What distinguishes living things from dead and nonliving things? No single characteristic is enough to define what is meant by "life." In this session, five characteristics are introduced as unifying themes in the living world.
Session 2 Classifying Living Things
How can we make sense of the living world? During this session, a systematic approach to biological classification is introduced as a starting point for understanding the nature of the remarkable diversity of life on Earth.
Session 3 Animal Life Cycles
One characteristic of all life forms is a life cycle — from reproduction in one generation to reproduction in the next. This session introduces life cycles by focusing on continuity of life in the Animal Kingdom. In addition to considering what aspects of life cycles can be observed directly, the underlying role of DNA as the hereditary material is explored.
Session 4 Plant Life Cycles
What is a plant? One distinguishing feature of members of the Plant Kingdom is their life cycle. In this session, flowering plants serve as examples for studying the plant life cycle by considering the roles of seeds, flowers, and fruits. A comparison to animal life cycles reveals some surprising similarities and intriguing differences.
Session 5 Variation, Adaptation, and Natural Selection
What causes variation among a population of living things? How can variation in one generation influence the next generation? In this session, variation in a population will be examined as the "raw material" upon which natural selection acts.
Sessions 6 Evolution and the Tree of Life
Why are there so many different kinds of living things? Comparing species that exist today reveals a lot about their relationships to one another and provides evidence of common origins. This session explores the theory of evolution: change in species over time.
Session 7 Energy Flow in Communities
Communities are populations of organisms that live and interact together. The structure of a community is defined by food web interactions. The process of energy flow is the focus of this session as the interactions between producers, consumers, and decomposers are examined.
Session 8 Material Cycles in Ecosystems
Studying an ecosystem involves looking at interactions between living things as well as the nonliving environment that surrounds them. Life depends upon the nonliving world for habitat, as well as energy and materials. In this session, material cycles will be explored as critical processes that sustain life in an ecosystem.