Early Childhood Environmental Education (EECE) and Early Childhood Education for Sustainability (ECEfS) are becoming increasingly integrated into preschool curricula, highlighting their key role in shaping environmentally conscious and sustainably oriented generations from an early age. The mentioned concepts represent the theoretical starting points of this empirical quantitative study, the aim of which is to examine the differences in the implementation of ESD, as well as the differences in the achieved outcomes of Education for Sustainable Development (ESD) in kindergartens with and without eco-programs, based on the preschool teacher's assessment, and to identify the specifics of the implementation of ESD in kindergartens with an ecoprogram in Slovenia. The research was conducted in 2024, on a sample of 114 preschool teachers employed in Slovenian kindergartens. The results confirm that in kindergartens with an eco-program, ESD's ecological, social and economic dimensions are successfully connected, and an integrated approach is applied. In kindergartens with an eco-program, ECEfS is implemented more prominently in the regular curriculum, and the outcomes of ECEfS are achieved to a higher degree than in kindergartens without an eco-program, which indicates the success of the program from the point of view of sustainability.