This article reports findings from a case study of the practical application of a standardisation tool in everyday social work practice. The example tool used herein is the Swedish version of the UK-based Integrated Children's System, which in Sweden is known as Children's Needs in Focus (Barns Behov i Centrum; BBIC). The study analyses group and individual interviews with social workers, managers and politicians using concepts from implementation research and the micro-sociological concept of accounts. The findings demonstrate how participants describe and explain their deviations from the BBIC manual and from the more informal intentions of the tool. Such deviations are conditioned by the fact that professionals often employ their own discretion in their work, which is necessarily inherent in human service occupations such as social work. Although the BBIC was initially well received, the professionals describe how that reception eventually turned to scepticism and a more critical stance toward the manual. This can be attributed to both absence of significant necessary implementation conditions and key organisational factors as well as a lack of compatibility between the tool's construction and users' needs and expectations. This article also discusses the general socio-technical and organisational implications of these findings.