The purpose of this study was to determine the relative effectiveness of pictorial drawings and scale models in teaching principles of orthographic projection. A sample of 60 students were randomly selected from a population of sixth grade boys in four Minneapolis public schools. They were divided into three IQ levels and assigned to four groups: (1) scale model group, (2) pictorial drawing group, (3) no aid group, and (4) control group. An orthographic projection test was developed and pilot tested on naive seventh graders. A rear screen slide projection apparatus was developed to present problems in a "learning task" and in a "transfer task." Data collected involved the number of responses and statements of reasons for choice selection. Analysis of variance techniques were used for the analysis. Findings included: (1) The pictorial drawing group performed significantly better than the other three groups on the "transfer task," (2) There was no difference between ability levels on the "transfer task," (3) Learning efficiency was significantly better for the high ability level over the low ability level, and (4) There was no significant difference in learning efficiency between scale model and pictorial drawing groups. This thesis was submitted to Minnesota University. (EM)