Stages of Language Development: First Words, Multiple Word Utterances, Grammatical Morphemes (continued)

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The fact that children apply morphological rules productively can be verified by a test devised by Jean Berko (1958), known as the wug test. In this type of experiment, children are shown pictures that are described using nonsense words, such as the noun wug. A child might be shown a picture of one of these and then be asked to describe a picture with two. If the child says they are two wugs, then we know he/she has learned the rule for making plurals, since no adult has ever said wugs to the child before. Similarly, the rule for forming the past tense of verbs might be tested by showing a picture of a man blicking and then asking what the man did yesterday. If the child says he blicked, we know a rule is being applied.

These rules are learned by children, becoming part of their internalized grammars of their language, but the rules are not taught to them. Adults know the rules, of course, or they would not be able to produce the correct morphology. But their knowledge is not conscious. And even if you do know the rules in some conscious way (as you now do), you would not be able to teach them to a preschooler. Think, for example, about how you might teach the distribution of the allomorphs of the plural or the past tense using vocabulary that a preschooler would understand.