An attempt was made to determine differences in reading achievement gains and student attitudes towards school between groups of third grade children enrolled in either modified open or traditional classrooms in the same school. The Metropolitan Achievement Test in Reading was used for pre- and posttest comparisons of achievement, and a questionnaire on student attitudes was administered at the end of the school year. Radical differences in the kinds of children assigned to either modified open or traditional classrooms presented serious problems in data analysis. Children had been previously selected for inclusion in a particular classroom setting on the basis of scholarship and ability to adjust (slow learners and non-English speaking children were assigned to traditional classrooms). Therefore, a wide discrepancy was found in pretest reading ability. Also, the total number of children in the modified open classrooms greatly exceeded that of the traditional classrooms. Statistical modifications (described in detail) were made in an effort to cope with these population problems. Results indicated: (1) there were no significant differences in expected reading achievement gains for any group, and (2) there were no significant differences in pupil attitudes. Descriptions of classroom operations observed for both types of teaching approaches provide interesting comparisons. (ED)