Purpose The purpose of this study is to examine if there is a difference between service-sector Lean Six Sigma (LSS) project teams that progress through Tuckman’s group development model and those that do not in terms of the number of completed projects, the number of projects completed on time, the length of time to complete the projects and the total cost savings and avoidance because of the projects. Design/methodology/approach The research consisted of a quantitative, descriptive methodology. The design included a sample from a service-sector LSS practitioner population, a survey instrument, one independent construct with two levels, four dependent constructs and a multivariate analysis of variance (MANOVA). Findings The progression of service-sector LSS teams through Tuckman’s group development model, as measured with the group process questionnaire, significantly influences the teams in terms of the number of completed projects, the number of projects completed on time, the length of time to complete the projects and the total cost savings and avoidance because of the projects. Research limitations/implications A limitation of the study is there may be other factors not related to Tuckman’s group development model that can influence the outcomes of LSS projects. These variables may include senior executive buy-in, number of LSS practitioners in the organization, the robustness of LSS training programs, level of talent and other factors not related to Tuckman’s group development model. Another limitation of the study encompassed using a sample of convenience instead of a random sample. Practical implications The recommendation for practice is binate. First, service-sector LSS project teams should ensure they progress through the stages of Tuckman’s group development model to enjoy the significantly improved project outcomes. Second, LSS practitioners and trainers should ensure that Tuckman’s group development model is part of the training curriculum. Social implications The study demonstrates that all groups should attempt to progress through the stages of Tuckman and Jensen (2010) group development model to enjoy the benefits of working in a cohesive, task-focused team. Originality/value This study adds to the body of knowledge because, prior to this study, there was not prior research involving Tuckman’s group development model and LSS team outcomes.