What Do Development Banks Learn from Their Operations? A Textual Analysis of Project Completion Reports from the IDB

Multilateral development banks require operational teams to document “lessons learned” at project closure, yet little is known about the collective architecture of the institutional learning these systems produce. This paper analyzes a corpus of 6,620 lesson statements from Inter-American Development Bank (IDB) Project Completion Reports published between 2014 and 2024, applying multilingual sentence embeddings, density-based clustering, and topic modeling, and examines sectoral and temporal patterns through fixed-effects regressions. Three findings emerge. First, codified learning is highly concentrated: more than 93 percent of lessons fall within a single dominant thematic area centered on project design and implementation management, a pattern observed across all sectors. Second, this concentration remains broadly stable from 2018 to 2024, although its internal composition shifts gradually toward monitoring and evaluability concerns. Third, lessons are largely prescriptive but less consistent in assigning responsibility: fewer than one in three both identify a specific actor and use normative language. The results suggest that operational lessons in Project Completion Reports capture a substantive but relatively concentrated dimension of operational experience. Preserving greater contextual specificity, making responsibility more explicit, and strengthening the mechanisms that connect accumulated lessons to future operational decisions could strengthen their contribution to institutional learning.