This study assessed the effectiveness of a spatialized mathematics intervention on the mathematical performance and spatial visualization skills of students from an underprivileged Indonesian community. Grade 8 students (N = 407) were assigned to one of twelve experimental classes, receiving the spatial mathematics intervention, or one of seven control classes, continuing with the standard mathematics curriculum. Prior to and following the intervention, a pre-test and post-test design was administered. The data were analyzed using Analysis of Covariance to ascertain the effect of the intervention. Results revealed that the students in the experimental group exhibited significant improvements in spatial visualization skills and mathematics performance (including both spatial and non-spatial competencies), compared to the control group. Importantly, the findings provide evidence that the transfer effects of the spatialized curriculum occur differentially for students of varying ability levels. The findings highlight the importance of spatial intervention in enhancing mathematics performance and spatial visualization skills. The study suggests potential avenues for a paradigm shift in mathematics education that recognizes and embraces the profound influence of spatial thinking.