The primary and secondary learning years shape development of scientific interest and skills required for science literacy, presenting a critical timeline target for science education intervention. Although many initiatives exist to target this timeframe, the modern classroom belies easy scientific investigation. Numerous initiatives often run simultaneously in a given classroom, creating limited capacity for variable control. Consequently, there is a dearth of high-quality and meaningful data in education sciences that exacerbates the general segregation of education research from practice. Many science reform programmes go unmeasured. The limited number that is researched often report strictly qualitative results or stop short of statistically significant quantitative investigation. Lack of high-resolution data restricts the ability to make informed policy changes and precludes attainment of “evidence-based education”. Here, we demonstrate 5-year efficacy of a novel, inquiry-based primary and secondary science reform programme Integrated Science Education Outreach (InSciEd Out). Five years of data over three cohorts of matched students from US grades 5–8 show maintained gains in science fair and honours biology election, as well as improved performance on Minnesota state standardized science testing. Detailed value-added analyses further reveal InSciEd Out-correlated gains in partnership-focused areas of life sciences, and history and nature of science. These analyses provide evidence that scientifically rigorous evaluation demonstrating relevant programme efficacy is indeed achievable in education science. Our results support the premise that the InSciEd Out programme is a scalable intervention capable of primary and secondary science education reform. The programme substantively builds upon prior efforts in the field. Although InSciEd Out deploys novel approaches and tools, the broad lessons learned from this programme are readily translatable to other contemporary efforts cultivating science literacy for all.