The central aim of this descriptive and exploratory study is to empirically examine the views and perspectives of practitioners working with young people in the youth justice system in England and Wales. Based on a case study of Peterborough youth offending service (PYOS), the study adopts a multi-method approach. Interviews with 22 practitioners, observations of their practice and key documentary evidence are reviewed, which identify the processes involved in the core practice of key practitioners and a deeper understanding of how policy and legislation reform are experienced in practice. Practitioners play key roles as case managers in the intervention process, yet youth justice literature somewhat neglects the role and perspective of staff within multi-agency youth offending teams (Case, 2007), despite increasing focus on youth justice practice through organisational analyses (see for example, Burnett and Appleton, 2002; 2004a; Field, 2007; Holdaway et al., 2001; Newburn et al., 2002; Souhami, 2007; Stahlkopf, 2008), and much critique of youth justice policy in England and Wales (see for example, Goldson, 2002; Goldson and Muncie, 2006; Pitts, 2003; Smith, 2007). The central argument of this thesis is that knowledge (what is known about effective practice) is not applied effectively in practice. Questions are raised regarding the use of professional discretion and the accountability of practitioners working with young offenders within a perceived managerialist process which neglects individuals needs in favour of achieving targets and performance measures. The findings of this study support the view that the use of standardised assessment tools increase accountability of practitioners whilst reducing their professional discretion, which constrains practice. A lack of structural support created a cultural divide between management and practitioners, which further confounded their practice. Practitioners face a multitude of obstructions to their work with young people, which seem to be further rooted in the prioritisation of recording information and meeting targets, which results in less time attributed to planning and delivering interventions. In a climate of uncertainty for the youth offending service (YOS), in which doubts about its future are frequently raised and further reductions are made to YOS budgets, there is increased need for well-informed and supported practitioners to be working with young people who offend.Darwin College, the Economic Social Research Council, and the Institute of Criminolog