Spatial visualization is not yet clearly understood. Some researchers have concluded that two factors or abilities are involved, spatial orientation and spatial visualization. Different definitions and different tests have been proposed for these two abilities. Several studies indicate that women generally perform more poorly on spatial tests than do men; it has been suggested that this sex difference has an hereditary basis. Several studies support this hypothesis. A study has shown that females with Turner's Syndrome perform much more poorly on Wechsler performance subtests than on the verbal subtests, but immaturity due to parental indulgence may account for these results. A research question of considerable interest is at how early an age spatial ability can be tested. Few attempts have been made to improve performance on spatial tests by practice or relevant training, but the author has such a study with third and fifth graders underway. Such studies have shown training to improve scores considerably. References are provided. (KM)