The results of a STEM educational program named "The air we breathe" implemented in a primary rural school in Greece as part of a National Research Project entitled "Diffusion of STEM (DI-STEM)" are presented in this paper. The educational program deepened in air pollution and intended to foster students' eight scientific practices proposed by the NGSS. Results derived from students' pre-post test questionnaires revealed great progress in five of the scientific practices (evaluating appropriate methods and tools for collecting data, developing & using models, constructing explanations, engaging in argument from evidence and evaluating & communicating using tables, diagrams, and charts) and moderate progress in three of the scientific practices (asking questions and defining problems, planning & carrying out investigations, and using mathematics). The implications for successful STEM education in primary education are discussed.