INVESTIGATED WERE JUNIOR HIGH SCHOOL STUDENT'S UNDERSTANDINGS OF THE CONCEPTS INTRINSIC TO PROBABILITY THEORY. THE SPECIFIC OBJECTIVES WERE TO EXPLORE (1) THE VARIATION AND CONSISTENCY IN USAGE OF QUANTITATIVE LANGUAGE TERMS, (2) THE ABILITY TO GENERATE POSSIBLE COMBINATIONS AND PERMUTATIONS, (3) THE RECOGNITION AND UTILIZATION OF THE CONCEPT OF INDEPENDENCE OF EVENTS, (4) THE ABILITY TO APPROPRIATELY ASSESS, AND MODIFY, CONTINGENCY RELATIONS IN A COMPLEX SET OF RELATED EVENTS, AND (5) THE EFFECT OF VARIATION IN EVENT-STRUCTURES OF PROBABILISTIC EVENT-SETS ON ESTIMATION OF POPULATION PARAMETERS AND SUBJECTIVE CERTAINTY OF THESE ESTIMATIONS. EXPERIMENTAL PROCEDURES WERE DESIGNED TO OBTAIN DATA ON EACH OF THESE OBJECTIVES. RESULTS INDICATED THAT THE STUDENTS FAILED TO UNDERSTAND THE BASIC IDEA OF PROBABILITY THEORY. RECOMMENDED ARE THAT FURTHER RESEARCH BE UNDERTAKEN ON (1) PARTICULAR CONCEPTS SUCH AS PERMUTATION, CORRELATIONS, AND OTHERS, AND (2) DETERMINING THE EXPERIENCE NECESSARY FOR THE ACQUISITION AND UTILIZATION OF APPROPRIATE QUANTITATIVE LANGUAGE TERMS. (DS)