["European Journal of Education, Volume 61, Issue 2, June 2026. ", "\nABSTRACT\nInterdisciplinarity is often cast as a normative route to both scientific and societal impact, yet its ‘returns’ remain persistently contested. A key reason is empirical identification: prior work frequently collapses thematic breadth (what problems and concepts a project spans) and cognitive distance (how far collaborators are separated in disciplinary training) into a single interdisciplinarity signal, while simultaneously absorbing differences in team organisation into the same measure. Estimated effects therefore conflate scope‐driven opportunities for recombination with coordination, translation and alignment frictions—costs that are not intrinsic to interdisciplinarity per se but arise from how collaboration is organised and governed. This study disaggregates interdisciplinary knowledge production into three analytically distinct elements: thematic diversity, capturing the breadth of topics a project traverses; cognitive diversity, capturing heterogeneity in team members' disciplinary backgrounds; and team assembly, modelled as an independent moderator that shapes integrative capacity even within single‐discipline projects. Using 31,370 Swiss National Science Foundation (SNSF)–funded projects (2009–2020), we measure Thematic and Cognitive Diversity with the Rao–Stirling index and link them to both theoretical and applied innovation while testing how team assembly conditions diversity returns. We find two distinct functional forms and a clear moderation pattern. Thematic diversity is associated with power‐law growth in innovation and is comparatively insensitive to team assembly. Cognitive Diversity exhibits an inverted U‐shaped relationship with innovation, and its payoff is strongly contingent on team assembly: benefits concentrate at moderate cognitive distance and weaken as integrative capacity increases. By disentangling scope, distance and assembly, the study reconciles competing claims about interdisciplinary returns and informs science policy and evaluation practice on aligning interdisciplinary ambitions with team design and governance mechanisms that can support both academic recognition and societal uptake.\n"]