Lexical Development of 18- to 35-Month-Olds: Vocabulary Size, Lexical Composition, and Late Talking

RESCORLA-001Dr. Leslie A. Rescorla is Professor of Psychology, Director of the Child Study Institute, and Director of Early Childhood Programs at Bryn Mawr College. Educated at Radcliffe, the London School of Economics, and Yale, she obtained her clinical training at the Yale Child Study Center, the Philadelphia Child Guidance Center, and the Children’s Hospital of Philadelphia.

Dr. Rescorla developed the Language Development Survey (LDS), a screening tool for language delay in toddlers. She has presented findings from her 15-year longitudinal study on late talkers in numerous publications. In addition to her research on language delays in young children and in longitudinal patterns of school achievement, Dr. Rescorla conducts research on empirically based assessment of emotional and behavioral problems in children, adolescents, and adults. Her recent paper, titled “Lexical development in Korean: Vocabulary size, lexical composition, and late talking” was published in the Journal of Speech, Language, and Hearing Research. The study is part of a broader research program that has also studied Greek and Italian LDS data, with additional studies in progress.

Background of the study

In this series of studies, we have compared typical and delayed lexical development of Italian, Korean, Greek and U.S. 18- to 35-month-olds. The current study is part of a broader cross-linguistic research program designed to test the utility of the Language Development Survey for characterizing both typical and delayed lexical development in other languages with respect to vocabulary size and lexical composition. To this end, we used the criterion of <50 words on the LDS to identify late talkers in each language and then compared these late talkers with younger vocabulary size-matched children.


The LDS can be adapted for use in other countries and yields results that are very consistent across cultures/languages:

  • Vocabulary size increases with age but there is wide variation in children of the same age
  • Girls have larger reported vocabularies than boys

  • American children seem to have larger reported vocabularies than children in other countries in the youngest age group but not later

  • Children within the same language/country tend to be learning the same words

  • There is a lot of similarity across languages/countries in the earliest/most common words acquired – but cross-language concordance is lower than within-language concordance, probably mainly for cultural reasons but also possibly linguistic ones

  • The LDS can easily identify late talkers in other languages

  • Late talkers are learning the same words as younger typically developing children, they just do it later.


The top 50 words children acquire seem pretty “universal” and so are good targets for intervention for children who are slow to talk; children who have <50 words by 24 months are showing vocabulary delay and parents should discuss this with their pediatrician.  If receptive language is also delayed  at 24 months, intervention should be sought right away. However, if receptive skills are normal and there are no other concerns except late talking, then intervention can be deferred until 30 months or so, as the child may soon start talking.

Public reception and next steps

When reports get in the media, people seem interested in this work and contact me. When I presented some of the Korean results at AAAS in Vancouver, some British journalists picked it up – they focused on the “top words every kid should know” angle – and this was picked up in dozens of papers and on some TV spots and many people wrote to me.

I plan to do more pair-wise cross-linguistic studies and then aggregate all the languages we have in a multinational analysis

About the department

I am in a psychology department with 7 faculty members. It is a small department, so I am the only member who studies language.  At the Child Study Institute, we evaluate and treat many late-talking toddlers, as well as children with autism spectrum disorders (www.brynmawr.edu/csi). Also, we have a department school where we have a Language Enrichment Preschool Program and kindergarten for children with language delays (http://www.brynmawr.edu/thorne/programs/preschool.html#LEPP)