The development and literacy skills in children who speak Spanish is a major problem for our society. The most pressing issue for research in this area is the language in the literacy development of English-language learning. The objective of this program project application is to identify the factors and conditions under which children who speak Spanish develop proficient literacy skills in English and Spanish. The central theme is that there is substantial variability in the development of literacy skills among English-language. Multiple factors and conditions at levels involving the child, teacher, and the context in which the child develops (school, family, community) account for this variability. In order to explain this variability, these factor and conditions must by language in literacy skill development. To address this objective and central theme, we propose a core longitudinal study from K-G3 of 1,440 children in 144 classrooms in schools from 3 geographic regions: urban Texas, border Texas, and urban California. These children will be selected from classroom representative of one of 4 language program models; (1) English language immersion; (2) early exit; (3) late exit; and (4) dual language. Five projects are proposed: 1) Project I (Measurement) addresses the development and evaluation of instruments for measuring oral language proficiency, literacy skills, and literacy-related skills in English and Spanish; 2) Project II (Development) proposes a 4-year longitudinal study (K-G3) of the growth of oral language proficiency, literacy skills, and literacy-related skills; 3) Project III (Instruction) provides for systematic observations of classroom instructional practices; Project IV (Intervention) evaluates the efficacy of early interventions for high risk English-language learners. Two Cores support the 5 projects: Core A (Administrative Core); and Core B (Data Management, Computer, and Statistics). Projects II-IV are based on the same core longitudinal sample and utilize the measures developed in Project I (Measurement). This synergistic, multi-site study addresses the primary focus of the RFA by systematically evaluating "the condition under which English-language reading and writing skills are most efficiently and productively developed in children whose first language is Spanish."