Literature and our experience provide evidence for the motivating effect of real-life STEAM projects. This study tries to unveil factors that may explain this effect. This study is based on a case study involving two lower secondary school classes engaged in a house modelling project including the stages: drawing the plans, modelling and 3D printing the house and putting the activity in the context by networking with another school and a local company. Data were collected from questionnaires, interviews and classroom observations to study students’ motivation, and the results of the Austrian National Competency Test (IKM Plus) are considered to refer to changes in learning results. Data analysis shows that working in teams, having more time to work on a meaningful task, and creativity seem to be the most important. The results of IKM Plus show a significant increase in comparison with the Austrian national average, however, defining the reasons needs further research.