JSLHR Research Article Identifying the Dimensionality of Oral Language Skills of Children With Typical Development in Preschool Through Fifth Grade Christopher J. Lonigan a and Trelani F. Milburn b Purpose: Language is a multidimensional construct from prior to the beginning of formal schooling to near the end of elementary school. The primary goals of this study were to identify the dimensionality of language and to determine whether this dimensionality was consistent in children with typical language development from preschool through 5th grade. Method: In a large sample of 1,895 children, confirmatory factor analysis was conducted with 19–20 measures of language intended to represent 6 factors, including domains of vocabulary and syntax/grammar across modalities of expressive and receptive language, listening comprehension, and vocabulary depth. Results: A 2-factor model with separate, highly correlated vocabulary and syntax factors provided the best fit to the data, and this model of language dimensionality was consistent from preschool through 5th grade. Conclusion: This study found that there are fewer dimensions than are often suggested or represented by the myriad subtests in commonly used standardized tests of language. The identified 2-dimensional (vocabulary and syntax) model of language has significant implications for the conceptualization and measurement of the language skills of children in the age range from preschool to 5th grade, including the study of typical and atypical language development, the study of the developmental and educational influences of language, and classification and intervention in clinical practice. Supplemental Materials: https://doi.org/10.23641/ asha.5154220 I n language research, the assumption of multidimen- sionality is alluded to across a number of topics, in- cluding the emergence of language in young children (Sénéchal, Pagan, Lever, & Ouellette, 2008), specific lan- guage disorders (Ramus, Marshall, Rosen, & van der Lely, 2013; van der Lely, 2005), reading and reading disorders (Nagy, Berninger, & Abbott, 2006; Perfetti & Stafura, 2014), cognitive disorders associated with aging (Burke & Shafto, 2008), and bilingualism (Bialystok, 2001; Chen, Ramirez, Luo, Geva, & Ku, 2011). In some studies, mea- sures of multiple language components (e.g., vocabulary, syntax) are used to represent distinct language dimensions in analyses with the expectation that one or more of these dimensions is responsible for outcomes in a different do- main (e.g., reading). In other studies, multiple measures of language are used to identify the effects of treatment or re- mediation for discrete dimensions of language. The extent to which these abilities are independent of one another as discrete skills, however, is unclear (Tomblin, Nippold, Fey, & Zhang, 2014), as is the extent to which specific measures are able to quantify children’s abilities on a single dimen- sion. The purpose of this study was to determine the dimen- sionality of a broad range of language skills in a sample of children with typical development in preschool through fifth grade by using a battery of language measures with sufficient measures to identify multiple underlying dimensions. Empirical Support for the Dimensionality of Oral Language Skills In their seminal study, Tomblin and Zhang (2006) examined the dimensionality of oral language across domains (i.e., vocabulary, grammar) and modalities (i.e., expressive, receptive) in a mixed sample of children with typical develop- ment and with language impairment in kindergarten, second, fourth, and eighth grades. In a comparison of one- versus two-factor models using confirmatory factor analysis (CFA) of multiple subtests from commonly used standardized lan- guage tests, a one-factor model fit as well as a two-factor a Department of Psychology and The Florida Center for Reading Research, Florida State University, Tallahassee b The Florida Center for Reading Research, Florida State University, Tallahassee Correspondence to Christopher J. Lonigan: email: lonigan@psy.fsu.edu Editor: Rhea Paul Associate Editor: Catherine Moran Received November 20, 2015 Revision received June 1, 2016 Accepted February 10, 2017 https://doi.org/10.1044/2017_JSLHR-L-15-0402 Disclosure: The authors have declared that no competing interests existed at the time of publication. Journal of Speech, Language, and Hearing Research • Vol. 60 • 2185–2198 • August 2017 • Copyright © 2017 American Speech-Language-Hearing Association 2185