Finnish legislation and policy on early childhood education and care (ECEC) express sustainability as a basic value. The national core curricula state that, during their years in ECEC, all children have the right to develop necessary values, knowledge and skills for living a sustainable life. Furthermore, early years education should be permeated by the principles of sustainability. However, research suggests that there is unclarity concerning how sustainability can be implemented in practice and pedagogy (Repo et al., 2018; 2019; Furu, forthcoming). Hence, the aim of this study was to explore how sustainability is currently done in ECEC settings in Finland. Further, we wanted to look into how the use of the recently developed "Assessment Tool for Promotion of Sustainability in ECEC" (PROSUS) by Furu and Valkonen (2020) might enhance sustainability work among teams (n=15) in ECEC settings in Finland. Based upon the findings, sustainability education is understood and implemented variably by the teams. This indicates that children are provided unequal opportunities for developing the basic capacities needed for leading a sustainable life. The study also makes visible how the PROSUS might enhance collegial learning regarding sustainability work and underlines the importance of collaborative practices in developing sustainability education in the early years' context.