A number of studies have lent support to the sex-linked major gene theory of spatial ability. Expectations arising from this theory (although not necessarily unique to it) are that spatial ability can be measured in children, that it is the same as spatial ability in adults, and that an individual's position in a distribution of spatial ability remains unchanged over time. Results of a longitudinal experiment utilizing test scores of 76 high school students and their earliertest scores provide confirmatory evidence for these expectations.