THE OBJECTIVE OF THE REPORT WAS TO INVESTIGATE AND EVALUATE CHILDREN, K-6, IN LANGUAGE DEVELOPMENT--ITS USE, CONTROL, AND EFFECTIVENESS IN ORAL, WRITTEN, AND READING COMMUNICATION. THE STUDY WAS ALSO CONCERNED WITH DEVELOPING FUNDAMENTAL METHODS OF ANALYSIS TO AID THE SCIENTIFIC STUDY OF CHILDREN'S LANGUAGE FOR THE FUTURE. THE SAMPLES OF LANGUAGE WERE DRAWN FROM 338 PRIMARY SCHOOL CHILDREN AT REGULAR INTERVALS OVER A 4-YEAR PERIOD. TWO SUBGROUPS, REPRESENTING HIGH AND LOW LANGUAGE PROFICIENCY, WERE SELECTED FROM THE TOTAL GROUP. THE CONTROLLED INDIVIDUAL INTERVIEW SITUATION WAS IDENTICAL FOR ALL SUBJECTS. DATA INCLUDED RECORDS OF THE SUBJECTS' SPEECH, WRITING, READING, AND LISTENING AND INFORMATION ON HEALTH, MENTAL ABILITY, SOCIOECONOMIC STATUS, SCHOOL ACHIEVEMENT, AND SCHOOL ATTENDANCE. IN THE FIRST PHASE OF THE STUDY THE MOST IMPORTANT ACHIEVEMENT WAS THE ESTABLISHMENT OF THE OBJECTIVE METHODS OF ANALYSIS. BY COMBINING THE CONCEPT OF A SEMANTIC SYNTACTIC UNIT WITH PHONOLOGICAL METHODS OF SEGMENTATION, AND BY IDENTIFYING AND DEALING WITH THE NONCOMMUNICATIVE ELEMENTS, THE MAZES, A NEW AND USEFUL METHOD OF LANGUAGE ANALYSIS WAS SHAPED. IN THE FIRST 4 YEARS OF SCHOOLING, THE SUBJECTS SHOWED NOTABLE INCREASE IN FLUENCY, EFFECTIVENESS AND CONTROL, STRUCTURAL CONTROL, CONVENTIONAL USAGE AND GRAMMAR, COHERENCY THROUGH THE USE OF SUBORDINATION, TENTATIVE THINKING THROUGH THE USE OF PROVISIONAL AND CONDITIONAL STATEMENTS, READING AND WRITING, AND CONTROL OF MAZES, AND SHOWED A POSITIVE RELATIONSHIP AMONG THE LANGUAGE ARTS. (GC)