The Child's Ideas for 1. Investigating Materials

The Challenges in Learning about Materials

some of the most revealing properties of materials (e.g., their densities) are not ones that are directly given perceptually, but need careful construction

In everyday life, we immediately see and describe the world in terms of its large-scale objects. For example, upon entering a classroom, you notice the desks, chairs, computers, books, lunch boxes and other objects as well as the fish tanks, plants, children and their teacher. We need to immediately recognize these things because we interact with them in distinctive and important ways in our daily life. For example, you eat your food, but not your computer; you sit on your chair but (generally) not on your desk; you water the plants but not your books; you talk to your classmates but not your chair, etc. In keeping with their importance, our visual systems are designed to automatically pick out the distinct objects in a visual scene and our language systems have a large number of words for naming types of objects at multiple levels of description (e.g., furniture, chairs, desk chairs; animals, dogs, Golden Retrievers) as well as their salient properties (large/small, red/green, hard/soft, cold/warm), ways of behaving (rolls, walks, talks, eats, swims), and functions (holds lunch, used for sitting, writing, reading, etc.). Words for types of objects, their properties, and simple actions involving them are among the very first words that children learn.

Much less salient to children, though ultimately no less important, is the world of “materials” of which objects are made. When we are naming materials, we are calling attention to another level of description—one that focuses on the kind of stuff something is a made of (a formless aggregate of a particular type) rather than the individual, whole object itself (which has a distinct shape and function and that we can pick up and play with). Thus, whether we call something “wood” depends on whether it has the cluster of properties that we think characterizes wood, not whether it is large or small or whether it is a spoon or a chair. The same objects can be made of different kinds of stuff, and the same kinds of stuff can be used to make different objects.

Young children are not clueless about materials—even preschoolers have some words for naming different types of materials (e.g., milk, sand, wood)—but their knowledge about materials is implicit (rather than explicit) and not yet coordinated with their knowledge about objects. Research has shown that the first names for kinds of material that children learn are for liquids (water, milk) rather than for solids (wood, metal, glass), although they may have a few such names by age three or four. This may be because of an “object bias” for solids. When you see a wooden spoon, what is most salient is the whole object and what you can do with it, not what is made of. In contrast, when you see a puddle or a glass of water, what is most salient is the stuff itself and its properties (you get wet if you go in it) not the shape of the puddle. Learning about the materials that objects are made of is important because it provides children an opportunity to coordinate these two levels of description and construct a more explicit concept of “made of.”

Coming to understand and “see” the world in terms of the materials that objects are made of requires not only simple observation but also imagination, controlled thought and reasoning, careful inquiry and systematic investigation. Things that look different on the surface (if scratched or painted) could be made of the same material and some things that look superficially alike may in fact be made of different materials. As you cut something into smaller and smaller pieces, mold it, heat it or cool it, some of its observable properties change (it might go from being solid to a powder, from one shape to another, from something hard to something soft and runny). Is it still the same kind of material? How do we know?

Answering these questions is not simple, but involves active theory–building about materials, which is a long protracted process. It requires imagining and elaborating another level of description—the level of materials (wood, glass, plastic) that is distinct from the more salient whole object level of description (spoons, desks, trucks). And it involves explicitly coordinating these two descriptive levels when making such statements as “This truck is made of metal; This cup is made of plastic.” It requires learning about the distinctive properties of materials and then explaining some aspects of the behavior of objects in terms of the kinds of materials they are made of—for example learning that the cup breaks because it is made of glass or the ball bounces because it is rubber. Ultimately, some of the most revealing properties of materials (e.g., their densities) are not ones that are directly given perceptually, but need careful construction. Thus it requires that children move from initial, imprecise characterizations of properties of materials that conflate weight and density to more differentiated and precise characterizations in which weight and density are distinguished. Our units start children on this important process.

—Carol L. Smith