TO ASSESS DIFFERENCES IN READING ACHIEVEMENT, READING ATTITUDE, AND READING PROGRESS OF FIRST-GRADE CHILDREN OF HIGH AND LOW MENTAL ABILITIES DIFFERENT CLASSROOM ORGANIZATIONAL PATTERNS WERE USED. EACH ORGANIZATIONAL PATTERN PROVIDED A DIFFERENT LEARNING SITUATION OR "TREATMENT." THE STUDY SAMPLE CONSISTED OF 32 TEACHERS AND 810 CHILDREN WHO WERE HETEROGENEOUSLY ASSIGNED TO ONE OF THE THREE ORGANIZATIONAL PATTERNS--(1) MODIFIED INDIVIDUALIZED, (2) THREE-TO-FIVE GROUPS, OR (3) WHOLE-CLASS-LANGUAGE-EXPERIENCE. PRETEST MEASURES OF INTELLIGENCE, READINESS, AND PRESCHOOL EXPERIENCE WERE OBTAINED ON THE CHILDREN. AT THE END OF A 140-DAY PERIOD OF INSTRUCTION, MEASURES ON ACHIEVEMENT IN READING, ATTITUDE IN READING, AND PROGRESS IN WRITING WERE OBTAINED. POST-TEST RESULTS SHOWED NO SIGNIFICANT DIFFERENCES BETWEEN TREATMENTS ONE AND THREE, BOTH OF WHICH PRODUCED SIGNIFICANTLY HIGHER SCORES ON WORD MEANING, WORD STUDY SKILLS, AND ARITHMETIC THAN TREATMENT TWO. ANALYSIS OF THE RESULTS SHOWED THE TREATMENTS PRODUCED NO SIGNIFICANT DIFFERENCES WITH SUBJECTS OF MENTAL AGE ABOVE 77 MONTHS. STUDENTS BELOW A MENTAL AGE OF 77 MONTHS SHOWED DIFFERENCES FAVORING TREATMENTS ONE AND TWO EXCEPT IN ATTITUDE TOWARD READING WHICH FAVORED TREATMENT THREE. ONE SIGNIFICANT RESULT OF THE STUDY WAS THAT NO TEACHER USING THE LANGUAGE-EXPERIENCE APPROACH WITHOUT GROUPING WITHIN THE CLASS, WANTED TO RETURN TO THE TYPICAL THREE-TO-FIVE GROUP ORGANIZATIONAL PATTERN. (AL)