THE PROBLEM OF THIS RESEARCH WAS TO DEVELOP AND VALIDATE A K SCALE FOR A MOTIVATIONAL TEST BATTERY. APPROXIMATELY 4,200 11TH GRADE, MICHIGAN PUBLIC HIGH SCHOOL STUDENTS COMPRISED THE STUDY. PROTOCOLS OF ABOUT 300 IDENTIFIED OVER- AND UNDERACHIEVERS WERE USED. AN ANALYSIS WAS CONSTRUCTED TO IDENTIFY ITEMS ON WHICH UNDERACHIEVERS SCORE AS OVERACHIEVERS AND OVERACHIEVERS SCORE AS UNDERACHIEVERS. BOTH TYPES OF ACHIEVERS WERE RANDOMLY ASSIGNED BY SEX TO A VALIDATION AND A CROSS-VALIDATION SAMPLE. EVIDENCE OF VALIDITY AND RELIABILITY OF THE K SCALE WAS EXAMINED BY--(1) APPLYING THE K SCALE TO ALL MISCLASSIFIED OVER- AND UNDERACHIEVERS, (2) DETERMINING THE EFFECTS ON MOTIVATIONAL BATTERY DISCRIMINATING ITEM RELIABILITY BEFORE AND AFTER APPLICATION OF THE MALE AND FEMALE K SCALE, AND (3) DETERMINING THE EFFECTS ON MOTIVATIONAL BATTERY VALIDITY WITH STANDARDIZED GRADE-POINT AVERAGES BEFORE AND AFTER APPLICATION OF THE MALE AND FEMALE K SCALE. THE CONCEPT UNDERLYING THE K SCALE OF THE MINNESOTA MULTIPHASIC PERSONALITY INVENTORY WAS SUBSTANTIATED FROM THE STANDPOINT OF THE RATIONALE OF DEFENSIVE TEST-TAKING ATTITUDES. IT WAS CONCLUDED THAT THE K CONCEPT POSSESSES THE POTENTIAL FOR A DISCRIMINATION SCALE BETWEEN OTHER SUBTLE BEHAVIORAL PHENOMENA. FURTHER INVESTIGATION WAS RECOMMENDED, HOWEVER, BEFORE ACTUAL EMPLOYMENT IN TEST BATTERY INTERPRETATION. (JC)