During the nineteenth and twentieth centuries, thousands of minors were sent to juvenile reformatories, aimed at transforming ‘problematic’ youngsters into obedient citizens. While the history of reform schools is well documented, little is known about the emotional practices taking places within their walls. Drawing on extensive archival research, this research explores the changing patterns of emotions and power in Belgian reform schools between 1890 and 1965. The project focuses on the role of emotions in three domains: the psycho-pedagogical observation techniques that were applied in the reformatories; the interpersonal relations between the educators and the detained minors; and lastly the emotional practices of the detained minors themselves. Autobiographical documents not only offer insight in the detention experience, but also show how emotions became a site of contestation. Connecting methodologies from historical criminology and the history of emotions, this research offers a framework to study disciplinary institutions through the prism of emotions and power, therein enriching our knowledge of emotional practices of underprivileged groups in society.