THE ASSUMPTION THAT ONE-TENTH OF THE YEARLY GROWTH IN ALL ACHIEVEMENT AREAS TAKES PLACE EACH MONTH OF THE SCHOOL YEAR AND THAT ONE-TENTH OF THE YEARLY GROWTH OCCURS DURING THE SUMMER MONTHS WAS INVESTIGATED. THE STUDY WAS CONDUCTED IN CONNECTION WITH THE ANNUAL IOWA BASIC SKILLS TESTING PROGRAM IN THE STATE OF IOWA. MEDIANS FOR THE 11 SUBTESTS WERE ESTABLISHED AS OF JANUARY 15. ADDITIONAL ADMINISTRATIONS OF THE TESTS WERE CONDUCTED AROUND APRIL 15 AND OCTOBER 15. DATA BEARING ON SUMMER GROWTH WERE OBTAINED LATE IN MAY AND EARLY IN SEPTEMBER. THE SCHOOL-YEAR PHASE WAS CONDUCTED IN GRADES 3-4, 4-5, AND 5-6. THE SUMMER PHASE WAS CONDUCTED IN GRADES 5-6. THE EXPECTED DISTRIBUTIONS WERE OBTAINED BY INTERPOLATING BETWEEN THE DISTRIBUTIONS OBTAINED FOR THE SAMPLES IN THE JANUARY PROGRAMS. THE MEDIANS OF THE EXPECTED DISTRIBUTIONS WERE SIGNIFICANTLY DIFFERENT FROM THE MEDIANS OF THE OBTAINED DISTRIBUTIONS OF OCTOBER AND APRIL. FINDINGS INDICATED THAT THE ASSUMPTION OF UNIFORM GROWTH THROUGHOUT THE SCHOOL YEAR WAS QUESTIONABLE. NO ONE ALTERNATIVE ASSUMPTION APPEARED TO BE MORE APPROPRIATE. THE MAJOR RESULTS ARE SUMMARIZED IN TABULAR FORM. (RH)