Introduction Improvement science emphasizes the need to understand and enhance quality in complex service systems. While the field primarily has developed within healthcare, its expansion into social care requires deeper engagement with how quality is understood and enacted in practice. This study addresses this need by exploring how child welfare professionals in Sweden understand and enact "quality" in their everyday work with implications for improvement science in complex human service systems.Methods The study employed a qualitative, practice-oriented, and interactive research design. The data consisted of 28 semi-structured interviews with professionals in child welfare, an analysis seminar, and documents (such as a quality management system and quality reports). An inductive content analysis was conducted, constructing themes through systematic interpretation rather than predefined frameworks.Results The analysis identified two coexisting logics of quality: one emphasizing uniformity, the other emphasizing responsiveness to uniqueness. The findings show how professionals move between these logics as tensions become salient in daily practice.Discussion By conceptualizing quality as a paradoxical construct, the study highlights how quality in child welfare is enacted through the ongoing negotiation of multiple logics, with implication for improvement science. The findings align with previous research suggesting that sustainable improvement involves the interplay of generalizable and contextual knowledge, and that paradoxes in organizational life shape conditions for learning and improvement.Conclusion Quality in child welfare is not a fixed attribute but a negotiated phenomenon, shaped by persistent tensions between uniformity and responsiveness. Recognizing these paradoxes invites reflection on how improvement science engages with quality in complex human service systems, particularly in relation to the interplay between codified standards and professional judgment.