ABSTRACT Failed humanitarian projects provide us with an opportunity to shed light on the complex interactions and conflicts among international donors, humanitarian workers and local recipients. This article explores such a contested and terminated project in post-First World War Belgium. The Child Health Section (1922–24) was a US international development programme initiated by Herbert Hoover and the Commission for Relief in Belgium Educational Foundation. Its aim was to provide health education to school children. Despite reaching 113,136 Belgian children between the ages of six and 12 in 1221 schools across the country, the project was abruptly discontinued after only one year. This contribution examines why the development assistance programme failed by using a micro-historical approach combined with concepts from development studies. The well-kept records of the CHS on the enduring conflicts with Belgian administrations reveal how US assumptions about their role in transforming or modernizing Europe clashed with (the diverse) European views on their own post-war reconstruction. This case demonstrates that the shift from providing short-term, needs-based humanitarian assistance to investing in long-term international development assistance did not always go smoothly or uncontested in post-war Europe.