Although the psychological literature has demonstrated that spatial reasoning and mathematics performance are correlated, there is scant research on these relationships in the middle years. The current study examined the commonalities and differences in students' performance on instruments that measured three spatial reasoning constructs and two mathematics content areas. There were no gender differences in terms of performance on the three constructs that measured students' spatial visualisation, mental rotation and spatial orientation. There were strong positive relationships between the students' spatial reasoning and mathematics performance (r = 0.66), with over 44% of shared variance between the two dimensions. Our study highlights the importance of spatial reasoning in the mathematics curriculum and the necessary promotion of this dimension as a general numeracy capability.