This dataset supported an impact evaluation of an extracurricular STEM intervention organized by the VUB STEAM Academie. The study examined whether participation in a one-day STEM-workshop influenced secondary school students’ STEM-related attitudes, motivation and career aspirations. The intervention consisted of: a 3D design workshop at the VUB FabLab and a photonics laboratory visit at B-PHOT (Vrije Universiteit Brussel). The dataset assessed STEM-interest, STEM-identity, Intrinsic motivation, Identified regulation, Introjected regulation, External regulation and STEM-career aspirations. The goal was to evaluate the effectiveness of a short-term extracurricular STEM-experience in fostering students’ STEM-engagement and motivation and to identify potential differences across student subgroups.