THIS STUDY REPORTS THE FIRST PHASE OF A 5-YEAR LONGITUDINAL INVESTIGATION OF THE COMPARATIVE EFFECTIVENESS OF A HIGHLY STRUCTURED PRESCHOOL PROGRAM AND A TRADITIONAL NURSERY SCHOOL PROGRAM IN AMELIORATING THE LEARNING DEFECTS OF CULTURALLY DISADVANTAGED CHILDREN. THE HIGHLY STRUCTURED PROGRAM IS INTENDED TO OVERCOME PARTICULAR WEAKNESSES OF DISADVANTAGED CHILDREN, WITH PARTICULAR STRESS PLACED ON LANGUAGE SKILLS. THE 55 SUBJECTS WHO TOOK PART IN THE 2-MONTH STUDY WERE SELECTED FROM LOW SOCIOECONOMIC HOMES AND WERE ASSIGNED TO CLASSES IN SUCH A WAY THAT EXPERIMENTAL AND CONTROL GROUPS WERE MATCHED IN IQ, SEX, RACE, AND SOCIOECONOMIC STATUS. THE SUBJECTS WERE PRE- AND POSTTESTED WITH THE STANFORD-BINET INTELLIGENCE SCALE, THE ILLINOIS TEST OF PSYCHOLINGUISTIC ABILITIES, THE PEABODY PICTURE VOCABULARY TEST, AND THE FROSTIG DEVELOPMENTAL TEST OF VISUAL PERCEPTION, AND WERE POSTTESTED WITH THE METROPOLITAN READINESS TESTS. COMPARISONS INDICATED THAT (1) EXPERIMENTAL SUBJECTS SHOWED SIGNIFICANTLY GREATER PROGRESS IN MEASURED IQ, (2) OVERALL PROGRESS IN PSYCHOLINGUISTIC ABILITIES WAS ESSENTIALLY THE SAME FOR BOTH GROUPS, (3) THE CONTROL GROUP SHOWED SLIGHTLY HIGHER VOCABULARY GAINS, ALTHOUGH THE GROUPS DID NOT DIFFER SIGNIFICANTLY, (4) THE EXPERIMENTAL GROUP SHOWED GREATER GAINS IN VISUAL PERCEPTUAL DEVELOPMENT, AND (5) THE EXPERIMENTAL GROUP SCORED SIGNIFICANTLY HIGHER IN EACH AREA OF THE READINESS TESTS. THESE RESULTS SUGGEST THAT THE HIGHLY STRUCTURED PROGRAM IS MORE EFFECTIVE, BUT FINAL EVALUATION MUST AWAIT THE EVALUATION OF THE PERFORMANCE OF THE SUBJECTS IN SCHOOL. (DR)