This four-year effectiveness study focuses on the scale-up of a model of curricular and teacher professional development intervention aimed at improving science achievement of all students, especially English language learners (ELLs). The model consists of three basic components: (a) inquiry-oriented science curriculum, (b) teacher professional development for science instruction with these students, and (c) school resources for science instruction. The project's main goals are: (1) to evaluate the effect of the intervention on student achievement, (2) to determine the effect of the intervention on teacher knowledge, practices, and school resources, and (3) to assess how teacher knowledge, practices, and resources mediate student achievement. The project is conducted in the context of the Florida current science education policies and accountability system (e.g., adoption of the Next Generation Sunshine State Standards in Science, assessment of science at the fifth grade, a Race to the Top award state). The study draws on findings from research on a previous NSF-funded efficacy study (035331) in which the model to be scaled-up was tested in a single school district. The effectiveness study includes three (of 67) school districts as key partners, representative of racially, ethnically, linguistically, and socioeconomically diverse student populations; 64 elementary schools, 320 science teachers, and 24,000 fifth-grade students over a three-year period. Science learning is the primary subject matter, inclusive of life, physical, and earth/space sciences. Six research questions corresponding to three research areas guide the proposed scope of work. For the research area of Student Science Achievement, questions are: (1) What is the effect of the intervention on fifth-grade students' science achievement, compared to "business as usual"?, and (2) To what extent are the effects of the intervention moderated by students' English as a Second Language (ESOL) level, SES status, and racial/ethnic backgrounds? For Teacher Knowledge and Practices as a research area, questions are: (3) What is the effect of the intervention on teachers' science knowledge and teaching practices?, and (4) To what extent is students' science achievement predicted by school resources for science instruction? For School Resources for Science, questions are: (5) What is the effect of the intervention on school resources for science instruction?, and (6) To what extent is student achievement predicted by school resources for science instruction? To assess the effect of the intervention on students' and teachers' outcomes, a cluster-randomized-control trial is used, resulting in a total of 64 randomly selected schools (after stratifying them by school-level percent of ESOL and Free Reduced Lunch students). All science teachers and students from the 64 schools participate in the project: 32 in the treatment group (project curriculum for fifth grade, teacher professional development, and instructional resources), and 32 in the control group (district-adopted fifth-grade curriculum, no teacher professional development, and no instructional resources). To address the research area of Student Science Achievement, formative assessment items are used at the end of each curriculum unit, along with two equated forms of a project-developed science test (to be used as pre-and posttests) with both treatment and control groups, in addition to the Florida's Comprehensive Assessment Tests-Science. Data interpretation for this research area employs a set of three-level HLMs (students, nested in classrooms, nested in schools). To address the research area of Teacher Knowledge and Practices and School Resources for Science, the project uses three measures: (a) two equated forms of a 35-items test of teacher science knowledge, (b) a classroom observation instrument measuring third-party ratings of teacher knowledge and teaching practices, and (c) a questionnaire measuring teachers' self-reports of science knowledge and teaching practices. All measures are administered to both treatment and control groups. Data interpretation strategies include a series of HLMs with emphasis on the relevant teacher outcomes as a function of time, and of school-level mediating variables. External project evaluation is conducted by Concentric Research and Evaluation using quantitative and qualitative methods and addressing both formative and summative components. Project research findings contribute to the refinement of a model reflective of the new science standards in the State and the emerging national science standards. The value added of this effort consists of its potential to inform effective implementation of science curricula and teacher professional development in other learning settings, including ELLs and traditionally marginalized student populations at the elementary school level. It constitutes practically the only research study focused on the issue of scale-up and sustainability of effective science education practices with this student subpopulation, which has become prominent due to the dramatic growth of a racially, ethnically, and linguistically diverse school-aged population, low levels of U.S. student science achievement, and the role of science and mathematics in current accountability systems nationwide.