This project will explore a new approach to studying how the timing and nature of input might affect language acquisition--more specifically, the re-acquisition of a first language (L1) and the acquisition of a second language (L2). The proposed research will directly bear on important theoretical issues such as: whether, and how, early experience with a language can establish a learner's mental representation of the language in some fundamental and long-lasting way, how much of a language can be acquired without negative feedback (e.g., through merely overhearing and/or being spoken to), and how much of implicit childhood memory for the structure of a language can be recovered through re-acquisition. This project will examine whether, and how, various kinds of experience with a language during childhood affect people learn or re-learn that language during adolescence or adulthood. Two studies will assess: (1) possible long-term and unique benefits of what is learned during childhood, and (2) possible benefits of incomplete language experience. Language abilities of first-time adult/adolescent learners of Spanish will be compared to those of re-learners will different kinds of prior experience with Spanish (e.g., overhearing vs. being spoken to vs. speaking briefly; early vs. late exposure). This project will focus on two aspects of language that can be readily acquired by children but seem hard to be mastered by adults, namely, morphosyntax and phonology. In addition general speaking (e.g., story telling) and comprehension skills (understanding everyday conversations) will be examined. The project will also bear on important applied issues such as whether it is worthwhile to encourage children to speak their immigrant parents' native language when they might stop using that language within a few years, and whether language education programs for young children could have lasting and measurable benefits.