Investigated were: (1) sex differences in the ability of 20 boys and 20 girls between 8 and 9 years of age to draw a plan of their house; and (2) variables related to such differences. Subjects were tested on four Piagetian tasks (verticality, horizontality, and two Euclidean space tasks), plan drawing, and vocabulary. After children completed the tasks, they were shown three plans that they had drawn 6 months, 3 months, and 1 week before, and were asked questions about difficulty, plan quality, satisfaction, differences between plans and pictures, and experience. Findings indicated that boys were able to draw a plan of ground floor rooms, doors, windows, and stairs earlier than girls were. A questionnaire revealed that boys and girls had differing attitudes toward the task: girls who drew plans horizontally thought it was difficult to do and were dissatisfied with the results, whereas boys thought that the task was easy and were satisfied. Girls also responded differently from boys with regard to prior experience with plans. When plan drawing was taught to 34 children matched for age and ability with 28 children in a parallel class, sex differences were not found. One-third of the girls developed dramatically from drawing vertical plans to well-structured horizontal plans, responding as though they possessed the horizontality concept, but were too unsure of themselves to use it. Four appendixes provide supplementary data as well as the study questionnaire. (RH)