THE INTERNAL STRUCTURE OF A BATTERY OF ACHIEVEMENT AND INTELLIGENCE TESTS WAS ANALYZED TO ENHANCE THE DIAGNOSTIC VALUE OF THE BATTERY. CONSTRUCTION OF THE ACHIEVEMENT AND INTELLIGENCE TESTS WAS GUIDED BY A FACET DESIGN. THE RESEARCH HYPOTHESES WERE THAT--(1) STAGES OF DEVELOPMENT AND ACHIEVEMENT IN THE VARIOUS AREAS TESTED IN THE BATTERY EXIST, AND (2) CERTAIN KINDS OF SYSTEMATIC DIFFICULTIES CAN BE DIAGNOSED BY FACET DESIGN AND BY ANALYSIS OF TEST DISTRACTORS. DATA ANALYSIS WAS DONE USING THE GUTTMAN-LINGOES SCALOGRAM ANALYSIS I (MSA-I) AND THE GUTTMAN-LINGOES SMALLEST SPACE ANALYSIS I AND II (SSA-I AND SSA-II). THE STRUCTURE OF THE INTERRELATIONSHIPS HOLDING BETWEEN A BATTERY OF TESTS AND BETWEEN ITEMS OF A SUBTEST WERE INVESTIGATED USING SSA-I. RESULTS WERE CONSISTENT WITH EARLIER FINDINGS ON THE RELATIONSHIPS BETWEEN DIFFERENT SUBTESTS OF ANALYTICAL ABILITY AND APTITUDE ACHIEVEMENT. THE MSA-I ANALYSIS OF SUBTESTS AND OF INDIVIDUAL ITEMS REVEALED THE EXISTENCE OF STAGES OF ACHIEVEMENT FOR THE ARITHMETIC TEST. A SSA-II ANALYSIS OF THE ARITHMETIC TEST SHOWED THAT SUBJECTS TENDED TO MAKE SIMILAR TYPES OF ERRORS ON DIFFERENT ITEMS. (PS)