Purpose: This study asked if children's performance on language tests reflects different dimensions of language and if this dimensionality changes with development. Method: Children were given standardized language batteries at kindergarten and at second, fourth, and eighth grades. A revised modified parallel analysis was used to determine the dimensionality of these items at each grade level. A confirmatory factor analysis was also performed on the subtest scores to evaluate alternate models of dimensionality. Results: The revised modified parallel analysis revealed a single dimension across items with evidence of either test specific or language area specific minor dimensions at different ages. The confirmatory factor analysis tested models involving modality (receptive or expressive) and domain (vocabulary or sentence use) against a single-dimension model. The 2-dimensional model involving domains of vocabulary and sentence use fit the data better than the single-dimensional model; however, the single-dimension model also fit the data well in the lower grades. Conclusions: Much of the variance in standardized measures of language appears to be attributable to a single common factor or trait. There is a developmental trend during middle childhood for grammatical abilities and vocabulary abilities to become differentiated. These measures do not provide differential information concerning receptive and expressive abilities.