There is increasing evidence for the impact of spatial training on mathematics performance in early years of education, however little research has focused on secondary school environments, which are traditionally more discipline driven. In the present study, a large-scale classroom-based intervention saw the introduction of twelve hours of spatial training instead of standard mathematics instruction across a ten-week term with grade eight students. The intervention program was delivered by classroom teachers within the Experience-Language-Pictorial-Symbolic-Application (ELPSA) pedagogical framework (Lowrie & Patahuddin, 2015). Differences in spatial and mathematics performance after the intervention, assessed by Hierarchical Linear Modeling, indicated that the intervention group (thirty-two classes) improved on spatial reasoning and mathematics achievement significantly more than a business-as-usual control group (eight classes). Improvement was found across geometry and measurement and number and algebra content for the intervention group, relative to the control group. This study provides evidence for an effective implementation of spatial learning with impact on mathematics performance, led by classroom teachers in a secondary school context.