A Mississippi study examined the effects of two instructional techniques using the Ford power train unit as an instructional aid. Eight schools were randomly selected from a population of 33 vocational agricultural departments. Three schools with 10 students from each school were randomly selected and assigned to treatment A, traditional lecture-demonstration. Six schools with five students from each school were randomly selected and assigned to treatment B, small group self-study. Treatment A served as the control group. One school participated in both treatments. The experimental independent variables manipulated by the researchers were (1) the type of instruction and (2) mechanical aptitude. Dependent variables were cognitive psychomotor and attitude posttest scores. High mechanical aptitude students taught by the small group self-study technique scored significantly higher on a second posttest than low mechanical aptitude students taught by the lecture-demonstration technique. Traditional lecture-demonstration students had a better attitude toward their instructional technique regardless of the mechanical aptitude level. High mechanical aptitude students were most negative toward small group self-study and most positive toward the lecture-demonstration technique. (BPB)