[2] Gleason created the Wug Test, in which a child is shown pictures with nonsense names and then prompted to complete statements about them, and used it to demonstrate that even young children possess implicit knowledge of linguistic morphology.

Menn and Ratner have written that "Perhaps no innovation other than the invention of the tape recorder has had such an indelible effect on the field of child language research", the "wug" (one of the imaginary creatures Gleason drew in creating the Wug Test) being "so basic to what [psycholinguists] know and do that increasingly it appears in the popular literature without attribution to its origins.

[6] Most of Berko Gleason's professional career has been at Boston University, where she served as Psychology Department chair and director of the Graduate Program in Applied Linguistics; Lise Menn and Harold Goodglass were among her collaborators there.

[15] Gleason devised the Wug Test as part of her earliest research (1958), which used nonsense words to gauge children's acquisition of morphological rules‍—‌for example, the "default" rule that most English plurals are formed by adding an /s/, /z/, or /ɪz/ sound depending on the final consonant, e.g. hat–hats, eye–eyes, witch–witches.

[17][note 2] The Wug Test also includes questions involving verb conjugations, possessives, and other common derivational morphemes such as the agentive -er (e.g. "A man who 'zibs' is a ________?

)[17] Gleason's major finding was that even very young children are able to connect suitable endings‍—‌to produce plurals, past tenses, possessives, and other forms‍—‌to nonsense words they have never heard before, implying that they have internalized systematic aspects of the linguistic system which no one has necessarily tried to teach them.

[2]: 8  It is "almost universal" for textbooks in psycholinguistics and language acquisition to include assignments calling for the student to carry out a practical variation of the Wug Test paradigm.

[21] The Wug Test's fundamental role in the development of psycholinguistics as a discipline has been mapped by studying references to Gleason's work in "seminal journals" in the field, many of which carried articles referencing it in their founding issues:[2]: 4 A review of citation lists [for Gleason's paper] over the years gives an interesting mini-view of the evolution of developmental psycholinguistics...

In the first 15 years following publication, the article was extensively cited by researchers attempting to validate its utility and extend its finding to nontypical populations.

Among other conclusions, this study found that: In contrast, both male and female daycare teachers used language that was similar both quantitatively and qualitatively, with both focusing on a dialogue based in the present and on the immediate needs of the children.

[23] Gleason's research eventually extended into the study of children's acquisition of routines‍—‌that is, standardized chunks of language (or language-plus-gesture) that the culture expects of everyone, such as greetings, farewells, and expressions of thanks.

At the conclusion of a parent-child play period, an assistant entered the playroom bearing a present, in order to evoke routines from the children.

Thirty-two Turkish-English bilinguals judged the pleasantness of an array of words and phrases in Turkish (their first language), and in English (their second), while their skin conductance was monitored via fingertip electrodes.

This experiment employed the Story Completion Test (often used to probe a subject's capacity for producing various common grammatical forms) as well as free conversation and repetition to elicit speech from the subject; this speech was then analyzed to evaluate how well he used inflectional morphology (e.g. plural and past tense word endings) and basic syntax (the formation of, for example, simple declarative, imperative, and interrogative sentences).

The stories were so designed that a non–language-impaired person's response would typically employ particular structures, for example, the plural of a noun, the past tense of a verb, or a simple but complete yes-no question (e.g. "Did you take my shoes?").

There was considerable variation among consecutive repeat trials of the same test item, although responses on successive attempts usually came closer to those a normal speaker would have produced.

The study concluded that the subject's speech was not the product of a stable abnormal grammar, and could not be accounted for by assuming that he was simply omitting words to minimize his effort in producing them[37]‍—‌questions of significant theoretical controversy at the time.