Children residing in out-of-home care may be more vulnerable to exhibiting higher levels of externalizing behaviour (e.g., destruction of property, harm towards others) than children living with their biological parents. Extant literature illustrates that child specific features and foster parent characteristics have been found to have an effect on the externalizing behaviour of children in out-of-home care. This study is a secondary cross-sectional analysis of the Assessment and Action Record (AAR) data from the Ontario Looking After Children (OnLAC) project (2007-2008). The AAR is an outcome measurement tool that assesses seven dimensions (i.e., health, education, identity, family and social relationships, social presentation, emotional and behavioural development, and self care skills) in the lives of children residing in out-of-home care in Ontario. Analysis includes child level, foster parent level and worker level characteristics. Results suggest that child welfare workers with less formal education are more likely to work with children in out-of-home care who exhibit higher levels of externalizing behaviour. Further, children in out-of-home care who experience higher levels of foster parent negativity are more likely to exhibit higher levels of externalizing behaviour. Findings suggest the examination of child, foster parent, and worker level characteristics during the development and implementation of policy and practice.