This paper evaluates an educational intervention aimed at improving visuo-spatial and mathematical skills among primary school students and at reducing the gender gap in learning mathematics through teacher training and classroom use of building bricks. Using a randomized controlled trial on a sample of Italian schools, we find that treatment effects are stronger with longer exposure and in-person teacher training, and that the intervention’s effectiveness on students’ outcomes is mediated by teachers’ improvements in spatial orientation skills. Gender differences emerge, with girls benefiting mainly in visuo-spatial abilities and boys in mathematics.