This longitudinal study examines the relationship between students' knowledge-in-use performance and their performance on third-party designed summative tests within a coherent and equitable learning environment. Focusing on third-grade students across three consecutive project-based learning (PBL) units aligned with the Next Generation Science Standards (NGSS), the study includes 1067 participants from 23 schools in a Great Lakes state. Two-level hierarchical linear modeling estimates the effects of post-unit assessments on end-of-year summative tests. Results indicate that post-unit assessment performances predict NGSS-aligned summative test performance. Students experiencing more PBL units demonstrate greater gains on the summative test, with predictions not favoring students from diverse backgrounds. This study underscores the importance of coherence, equity, and the PBL approach in promoting knowledge-in-use and science achievement. A systematically coherent PBL environment across multiple units facilitates the development of students' knowledge-in-use, highlighting the significance of designing science and engineering practices (SEPs) and crosscutting concepts coherently and progressively, with intentional revisitation of disciplinary core ideas (DCIs). The study also investigates how the PBL approach fosters equitable learning environments for diverse demographic groups, offering equitable opportunities through equity-oriented design. Contributions include a coherent assessment system that tracks and supports learning aligned with NGSS, emphasizing the predictive power of post-unit assessments, continuous monitoring and tracking. The implications of context similarity and optimal performance expectations within units are discussed. Findings inform educators, administrators, and policymakers about the benefits of NGSS-aligned PBL systems and the need for coherent and equitable learning and assessment systems supporting knowledge-in-use development and equitable opportunities for all learners.