The objective of this research was two-fold. First, to determine the impact of a Science, Technology, Engineering and Mathematics (STEM) Education program on school performance amongst primary education students. Second, to identify the potential benefits of this program on the key competences of university students in Primary Education Teacher Training. The primary education students’ sub-sample, after being matched on key covariates, was randomly assigned either to the experimental (N = 25) or control group (N = 25). The university students’ sub-sample consisted of 26 students self-selected from the Primary Education Teacher Training degree. The intervention consisted of 20 two-hour weekly sessions of highly structured after-school tutoring delivered by previously trained university students. Although statistical significance was not reached for the hypotheses tested, notably, the results showed between small and moderate effect sizes (i.e., magnitude and direction of the program impact) for primary education students on core STEM subjects (e.g., mathematics d = 0.29, natural science d = 0.26), and for university students on some key employability competencies (e.g., action orientation d = 0.27 or team orientation d = 0.54).