PROJECT SUMMARY/ABSTRACT Children with developmental language disorder (DLD) struggle to learn new words and have smaller, shallower vocabularies than their peers with typical language development (TLD). Recent research indicates that the semantic structure of children’s vocabularies affects their ability to learn new words and the vocabularies of children with DLD and TLD differ in semantic structure. While children with DLD struggle in many aspects of word learning, including semantics, they find the encoding of phonological information–new word forms–to be especially difficult. The proposed research will compare the phonological structure of vocabularies between children with DLD and TLD and investigate how differences in phonological structure affect children’s ability to learn the forms of new words. The proposed work will use a combination of behavioral methods to quantify vocabulary structure and success in word learning for 7- to 9-year-old children with DLD, age-matched peers with TLD, and (younger) vocabulary-matched peers with TLD. Together, these methods will address three specific aims. Aim 1 is to quantify the extent to which differences in inter-connectivity in phonological structure – quantified using clustering coefficient, C – affects novel word learning. It is expected that children will be more successful in learning the forms of words in regions of their vocabulary with higher compared to lower inter- connectivity (high C > low C) and that this effect of inter-connectivity will be stronger for children with DLD compared to their peers with TLD. Aim 2 is to compare levels of C in the extant vocabularies of children with DLD and TLD. It is expected that the average levels of C will be higher in the vocabularies of children with DLD than their peers with TLD. Aim 3 is to determine whether atypicality in the phonological structure of children’s vocabularies affects word learning. It is expected that differences in individual C values calculated for each child will account for variability in children’s success in word learning. These outcomes will lay the foundation for future research to maximize the efficacy of vocabulary interventions for children with DLD by tailoring which words are taught based on differences in vocabulary structure at both the individual and group level. If funded, the project will assist the applicant in establishing an independent program of research investigating developmental differences in word learning that will inform early childhood interventions. The specific training goals of this project are to 1) gain expertise in participant recruitment, 2) develop computational skills in network science, 3) learn new behavioral methods, and 4) advance professional development. The research and mentoring experience of the co-sponsors as well as the extensive resources of the sponsoring institution will contribute to the successful completion of both the proposed research and training goals.