The processes of educational planning and program development at the local and national levels differ in centralized and decentralized educational systems. In Türkiye, there is a centralized education system, and curricula are created centrally to include all students. In the United States of America, there is a nationally disseminated curriculum framework for science education and a set of standards developed in accordance with these frameworks, while curriculum development continues at the local level based on these two national documents. Seeing how the curricula are designed in the different systems and what details they provide to teachers would be a source for designing curriculum development policies. The purpose of this study is to provide a comparative description of the scope of curriculum documents and the details of the information they contain in two different systems. The research is a comparative, holistic, multi-case study conducted by analyzing curriculum documents at the national level. As a result of the research, national curriculum documents for science education in the United States contain comprehensive descriptions of expected outcomes and content, even as curriculum development continues to occur at the local level. In contrast, Türkiye's science curriculum describes expected outcomes and content in less detail. The outcomes are discussed in terms of curriculum elements, system diversity, and literature.