This study developed and field tested instructional units designed to help young adult farmers use farm management principles in decision making. Relationships were also sought between farmers' personal characteristics and their posttest scores. Ten teachers of vocational agriculture (Group A) received inservice training in using the instructional units; nine (Group B) received printed instructions but no training. A control group of nine teachers was also used. The units dealt with the relationship of goals to decision making, the principle of diminishing returns, fixed and variable costs, substitution, opportunity costs, and profitable enterprise combinations. A multiple choice posttest measured the farmers' understanding. Special questionnaires were used to determine the backgrounds and reactions of the farmers and their teachers. Prepared instructional units proved more effective than traditional methods. Group A slightly surpassed Group B, which in turn surpassed the control group. Young adult farmers' managerial and marital status, educational background, age and experience, and (for experimental subjects) the number of farm management meetings attended, were related to posttest scores. Teachers and students reacted favorably to most aspects of the instructional units. (LY)