Preposition knowledge is important for academic success. The goal of this project was to examine how different variables such as English input and output, Spanish preposition score, mother education level, and age of English exposure (AoEE) may have played a role in children's preposition knowledge in English. 148 Spanish-English children between 7;0 and 9;11 produced prepositions in English and Spanish on a sentence repetition task from an experimental version of the Bilingual English Spanish Assessment Middle Extension (Peña, Bedore, Gutierrez-Clellen, Iglesias & Goldstein, in development). English input and output accounted for most of the variance in English preposition score. The importance of language-specific experiences in the development of prepositions is discussed. Competition for selection of appropriate prepositions in English and Spanish is discussed as potentially influencing low overall preposition scores in English and Spanish.