To evaluate the effectiveness of demonstrations in vocational agriculture instruction, 12 randomly selected Iowa high schools were divided and used as a control group and a demonstration group. Thirty-nine demonstrations were used in four subject matter areas of the test group, while the control group did not have use of the demonstrations. Analysis of variance of pretest scores revealed no difference between the students in their prior knowledge of subject matter. All analyses comparing the achievement of the vocational agriculture classes with and without demonstrations revealed no significant differences between the two types of instruction. However, analysis of covariance resulted in the demonstration group's adjusted mean posttest scores being higher than those for the control group in all four subject matter areas. This Ph.D. dissertation was submitted to Iowa State University. (Author/GB)