A test of the concept of horizontality was devised to examine the performance of a sample of 861 Australian school children in grades 1 to 6 tested in their classrooms. They were required to pencil in the water on eight outline drawings of a bottle standing at various angles. The concept was found to be quite difficult to attain, for not until age 10 years did more than 50% of subjects score well. A confusion of the horizontal and vertical was observed with some subjects, the confusion significantly occurring with those who had developed an appreciable understanding of the concept of horizontality, but were not fully operational.
