Supported accommodation, and congregate hostels in particular, remains the default form of provision for most young people experiencing homelessness, despite increasing evidence of its negative effects on residents. Existing evidence also suggests that such environments negatively impact hostel staff and thereby reduce their ability to provide effective support. The role of a keyworker in supported accommodation is to support and manage residents' behaviour. Because this behaviour is not always predictable and keyworkers operate independently, judgements cannot be universally applied and keyworkers must employ discretion in their decision making and response. However, there is a dearth of literature regarding the impact of this discretion on the keyworker role and the formation and implementation of organisational policy. This thesis aims to examine the influences on keyworkers' discretionary decision making and map the ways in which they respond to service users. It also explores how residents respond to this use of discretion, and the factors that influence their response. Rich qualitative data collected through participant observation, interviews, and focus groups conducted in three supported accommodation services within Scotland are used to examine the role of keyworker discretionary decision making in their responses to young residents. Drawing upon street-level bureaucracy, social control, and judgement and decision-making theory, this thesis develops an innovative conceptual framework through which to map out and deepen understanding of the keyworker-resident response dynamic. In doing so, it finds an irreconcilable tension within the keyworker role between: firstly, rule enforcer and, secondly, resident confidant. It argues that in conjunction with the high levels of discretionary decision making keyworkers hold, this constitutes an inherent and harmful impact of hostel accommodation for both residents and keyworkers. The thesis concludes by arguing against the continued use of the dominant congregate model of supported accommodation, while making recommendations that might mitigate the negative impact of discretionary decision making within these settings given the likely continued use of this form of provision.