This study examines the medicalisation of maladjustment in Britain, from the last years of the nineteenth century to the middle decades of the twentieth century. The study focuses on the conceptualisation and application of the tenn 'maladjusted', and the ways in which this reflected changing professional and lay perspectives of child behavioural problems throughout the early twentieth century. Examination of the process by which maladjustment was established as a medical category highlights the complex interplay between psychiatric, psychological, psycho-analytical, sociological, educational, and judicial theories and practices relating to child development. This study will show how a shifting emphasis on moral, intellectual and emotional development was reflected in the changing nature of theories relating to the behaviour of children. This process is explored from the introduction of psychological notions of mental and emotional adjustment in the 1890s, through the establishment of management strategies, including child guidance, in Britain in the inter-war period, the recognition of maladjustment as a statutory handicap under the 1944 Education Act, and, finally, to the publication of the Report of the (Underwood) Committee on Maladjusted Children in 1955. Focus on models of maladjustment illustrates the processes by which social factors, such as individual behaviour and parenting, became the subject of medical attention, highlighting issues surrounding increased intervention by the state and medical profession into the private domestic sphere. Examination of a range of primary and archival sources reveals how interest in the mental and emotional wellbeing of children came to dominate many key areas of policy-making throughout this period. This study challenges existing analyses which present the medicalisation process as one of harmonious teamwork, framed around shared agendas of child welfare and well-being. Despite the development of increasingly sophisticated medical and psychological theories of maladjustment, and greater understanding of child behaviour, professional focus on maladjusted children resulted in increased marginalisation of maladjusted children by the post-war period.