This study examines child and family social workers' application of knowledge. I have done a participant observation at a children and youth services department in a small Swedish municipality. I have investigated what kind of knowledge the social workers base their assessments on in the written document that is the result of a child care investigation. This study shows that, due to the acute character of their work, the social workers don´t have the necessary time for reflection which results in vague assessments. By not reflecting on their work to a sufficient degree, the social workers are not given the opportunity to fully understand their actions and relate their work to theoretical knowledge. The theoretical knowledge that they actually possess is not utilized in the written assessment. The social workers themselves say that they mainly use experience-based and tacit knowledge.