A study determined the effect of school organization on pupil attitudes, achievement, conceptual maturity, and classroom behavior. Ten teachers in each of three groups in a midwestern school district were selected and 707 pupils enrolled in their classes comprised the sample. An experimental group was placed in a nongraded form of organization, while control groups retained the traditional form of organization. The pupils in all groups were subdivided into three age groups: Normal age, underage, and overage. The results of tests administered to the students suggested the following conclusions: (1) The nongraded form of organization encouraged pupil development in conceptual maturity and participation in group activities, (2) teachers in the nongraded school were more tolerant of"disorderly pupil behavior" than were teachers in the graded schools, (3) the graded form of organization encouraged pupil development in achievement, attitude toward school, and contributing activities during usual teaching episodes, (4) the differences among the age groups were generally as expected, and (5) the behavior of the pupils identified as underage, normal age, and overage supported the multiage nongraded plan of organization. (HW)