IN THIS INVESTIGATION, AN ATTEMPT WAS MADE TO EVALUATE THE EFFECT OF SYSTEMATIC VARIATIONS OF SELECTED CONDITIONS OF REINFORCEMENT. EMPLOYED AS SUBJECTS WERE THREE GROUPS OF CHILDREN (MENTALLY HANDICAPPED, INTELLECTUALLY NORMAL, AND INTELLECTUALLY SUPERIOR), ALL OF WHOM HAVE MENTAL AGES (REVISED STANFORD-BINET, FORM L) WITHIN THE 9 TO 12-YEAR RANGE. EIGHT TASKS WERE INDIVIDUALLY ADMINISTERED TO THE SUBJECTS. THESE INCLUDED A VERBAL AND A CONCRETE FORM OF TASKS ASSUMED TO INVOLVE CONDITIONED RESPONSE LEARNING, DISCRIMINATION LEARNING, RATE LEARNING, AND PROBLEM SOLVING. THE PROPOSED CONDITIONS OF REINFORCEMENT WERE DEFINED AS TYPE OF REINFORCEMENT, FREQUENCY OF REINFORCEMENT, AND TIME OF INTRODUCTION OF REINFORCEMENT. THE DIMENSIONS OR VARIATIONS OF THESE CONDITIONS OVERLAPPED. THE ANALYSES OF THE DATA INVOLVED COMPARISONS BOTH WITHIN INTELLIGENCE GROUPS AND BETWEEN INTELLIGENCE GROUPS. A NUMBER OF RELATIONSHIPS PERTAINING TO LEARNING PERFORMANCE AND LEVEL OF ASPIRATION WERE REPORTED. (LP)