THE EFFECTIVENESS OF A NONGRADED HIGH SCHOOL WAS COMPARED WITH THAT OF A TRADITIONALLY GRADED HIGH SCHOOL IN THE SAME CITY BY ADMINISTERING TESTS AND RELATED EVALUATION METHODS TO A RANDOMLY SELECTED SAMPLE GROUP OF 141 TENTH-YEAR STUDENTS AT EACH OF THE SCHOOLS. SIX STUDENT GROUPS FOR EACH SCHOOL (DISTINGUISHED BY SEX AND ABILITY LEVEL) WERE USED TO COMPARE THE SCHOOLS ON SEVEN DEPENDENT VARIABLES REGARDING STUDENT ACHIEVEMENT, ATTITUDES, AND CRITICAL THINKING. ANALYSIS OF VARIANCE WAS APPLIED TO 63 HYPOTHESES, BASED ON THE ASSUMPTION THAT STUDENTS' RECORDS AT THE NONGRADED SCHOOL WOULD DIFFER SIGNIFICANTLY FROM THOSE AT THE GRADED SCHOOL BECAUSE OF THE NONGRADED SCHOOL'S DISTINCTIVE VERTICAL AND HORIZONTAL ORGANIZATION. NO SIGNIFICANT DIFFERENCES BETWEEN THE TWO SCHOOLS WERE FOUND WITH RESPECT TO GAIN IN READING COMPREHENSION, GAIN IN MECHANICS OF ENGLISH, ATTITUDES, OR CRITICAL THINKING ABILITY. GRADED STUDENTS GAINED SIGNIFICANTLY MORE IN MATHEMATIC REASONING THAN NONGRADED STUDENTS. THE OVERALL INTERACTION EFFECT BETWEEN THE SCHOOLS AND SEX AND BETWEEN THE SCHOOLS AND ABILITY LEVEL WAS NEGLIGIBLE. (JK)