Because of the general recognition of the importance of mathematics ability, and the close relationship between mathematics ability and spatial ability, eight studies were undertaken to discover and describe aspects of spatial competence in children. The range of abilities tapped stretched from very early precursor skills with Euclidean space to those requiring sophisticated manipulation of internal spatial images. The studies focused on two factors: spatial orientation and spatial visualization. Children from ages three to twelve years were included in the studies. Sex differences were studied across the sampling of skills and age ranges. In all studies, age was found to be a statistically significant factor. The major developmental trend across studies, indexed by the age factor, appeared to be a fairly linear quantitative growth pattern common to each. The result for the sex factor was also uniformly consistent: no significant sex differences were detected. (Author/BW)