Boston University is the home of psycholinguistics professor Jean Berko Gleason, who created the wug test in 1958 as a linguistics tool for testing how well children had learned the so-called "morphemes" associated with making nouns plural or verbs past tense. This process entails showing a child a series of fictional scenarios — like the first, one "wug" becoming two "wugs" — and then analyzing how well he or she pronounces the three "allomorph" sounds needed for plurality: "Z, "S" and "tZ." This test also gauges other types of morpheme learning, such as how well a student has truly learned the proper way to make verbs past tense or nouns possessive.
The three linguistic allomorphs for making nouns plural are the main thrust of the wug test. The first sound, "Z," is akin to the sound of "goggles" or "computers." The "S" allomorph is as it sounds too, like "rats" or "docks." Finally, the "tZ" sound is the most subtle, following sibilant sounds, as in "forces" or "stores."
Primarily younger elementary-age children are shown a series of 27 flashcards and are asked a series of questions about them. Since the pictures are depictions of imaginary animals with made-up names, it is impossible for children to properly make the word plural, past tense or possessive just because they may have learned how to conjugate that particular word before. For instance, with the first card the examiner tells a student, "This is a wug. Now there is another one. There are two of them. There are two ______." The student can only fill in that blank with the proper sounding "wugs" if he or she has truly learned which type of words receive this kind of treatment.
The wug test progresses through different types of allomorphs. Some questions test abilities to place some types of verbs into the past tense. Another flashcard shows a man holding an odd-looking object. "This is a man who knows how to rick," the examiner says. "He is ricking. He did the same thing yesterday. What did he do yesterday?" The child is expected to answer, "Yesterday, he ricked."
A different type of wug test question gauges how well a student can form a derived adjective. This card shows a dog covered with green spots. "This is a dog with quirks on him. He is all covered with quirks. What kind of dog is he? He is a _______dog." The student's answer should be "quirked."
The wug test is one of several tests that teachers can use to test a student's mastery of phonetic skills. All of these types of examinations are part of a field called morphology. Students of this field study and analyze the different morphemes, or basic phonetic units, of various words and parts of speech to find commonalities and anomalies. Professor Berko Gleason fully explains each flashcard of the wug test in The Child's Learning of English Morphology, which is available online.