Over 30% of children in the U.S. are dual language learners (DLLs) who are learning two languages. Understanding the development of both languages for young DLL children in early care and education is critical. However, few have simultaneously examined development of skills in both languages for children in preschool. Thus, the purpose of this study was to examine the language and literacy skills among Spanish–English DLL preschoolers and to directly compare change over time in language and literacy skills in both Spanish and English in secondary data analyses of three studies of DLL children. Hierarchical linear model analyses compared acquisition of language skills in English and Spanish in three studies. Using language and time as nesting factors, these models allow for direct contrast of level and rate of acquisition across languages. Results showed that Spanish-English DLL children made gains in their English abilities while being exposed to Spanish at home. Also, gains in English vocabulary skills were observed when children’s Spanish skills were higher than the English skills. Gains in children’s Spanish language abilities were not realized and children’s English language abilities did not appear to support children’s Spanish skills. Cross-language relations were observed in literacy. (author abstract)