The aim in this study was to determine the effectiveness of STEM-based robotic coding education for primary school students in terms of their decision-making skills. Mixed method research was conducted. Pretest-posttest control group designs were used in the quantitative phase, and a case study was performed in the qualitative phase of the research. The study sample consisted of 65 third graders. Pretesting of the experimental and control group students was performed using the decision-making skills scale. STEM-based robotic coding training was given to the experimental group for 6 weeks. Afterwards, the decision-making skills scale was applied as a posttest to both the experimental and control groups. The quantitative data were analyzed with paired and independent samples t-tests. A statistically significant increase was observed in the experimental group students' decision-making skills in favor of the posttest. There was no significant difference between the pre- and posttest scores of the control group students. An interview with 15 experimental group students was conducted to collect qualitative data, and the interview results were analyzed using content analysis. The robotic coding education positively affected the students' decision-making and problem-solving skills and their willingness to share ideas.