It is a widely held belief that mathematical content strands reflect different constructs which produce multidimensionality in mathematical achievement tests for Grade 3 through 8. This study analyzes the dimensional structure of mathematical achievement tests aligned to NCTM content strands using four different methods for assessing dimensionality. The effect of including offgrade linking items as a potential source of dimensionality was also considered. The results indicate that although mathematical achievement tests for Grades 3 through 8 are complex and exhibit some multidimensionality, the sources of dimensionality are not related to the content strands or the inclusion of several off-grade linking items. The complexity of the data structure along with the known overlap of mathematical skills suggest that mathematical achievement tests could represent a fundamentally unidimensional construct. Refining the definition of dimensionality to include detectable dimensionality is discussed.