There is limited research regarding what levels of proficiency in each language should characterize the language behavior of bilingual children and the impact of language exposure or language use variables on bilingual performance. This study was designed to examine the extent to which years of exposure to a language(s), amount of language input at home and at school, and amount of exposure to reading and other literacy activities in a language(s) relate to observed bilingual performance in young children, as obtained from parent and teacher reports. A secondary goal was to determine the extent to which parents or teachers could assist in determining language status by examining relationships between their ratings of the child's use and proficiency in the two languages and the child's grammatical performance. Fifty-seven children and their families were sampled from second grade classes of a large school district serving primarily low-income families in southern California. Multiple regression analyses for each language indicated that amount of Spanish input at home was a significant predictor of grammatical performance in that language. These input effects did not hold for English. Although there were some crosslinguistic differences, parent and teacher ratings of use and proficiency correlated with the child's grammatical performance in the target language. The findings suggest that parent and teacher estimates may be useful to determine bilingual status.