The establishment of the Central Observation Institute in Mol in 1913 marks the introduction of scientific expertise in Belgium's youth delinquency policy. The child at risk was subjected to a series of observations, resulting in an observation report ('waarnemingsverslag') that contained the psychological, moral and physical characteristics of the delinquent child, and suggested strategies for its re-education. This article focuses foremost on the technologies of observation in the first half of the twentieth century. In contrast to earlier research, the observation report is not used as a 'key to the past' but the article aims to historicise the observation report in its own right. Using M'charek's concept of 'folded object', the process of truth being created in the observation report is discussed, paying attention to the various actors at work in the reformatory and examining the dynamic relationships between the observation institution and the juvenile reformatories in the production and use of observation files.