The current study assessed reliability and validity evidence of the shortened Swedish Mathematics Anxiety Rating Scale--Elementary (MARS-E), using data from three time points. After initial pilot tests, a total of 429 students participated in the study, completing the MARS-E twice during grade 4 and once during grade 5. Confirmatory factor analyses supported a one-factor structure at each timepoint. The scale displayed both longitudinal and gender measurement invariance across timepoints, ensuring both stability and fairness across gender and time. Factor correlations with criterion variables were examined, revealing a strong correlation between math anxiety (MA) and test anxiety (TA) (r = 0.707). However, the two constructs had distinct relationships to other criterion variables, such as math performance (r[subscript ma] = - 0.343, r[subscript ta] = - 0.110) and self-concept in math (r[subscript ma] = - 0.580, r[subscript ta] = - 0.273). Gender correlations provided evidence of girls being more strongly associated with higher math anxiety scores compared to boys. The current paper provides evidence of the Swedish MARS-E as a valid, easily interpreted, unidimensional instrument for measuring math anxiety in Swedish primary school students. Additionally, the study highlights the gender disparities concerning math anxiety as early as grades 4 and 5.