This research study was designed to determine the effect of exposure to cultural-social-economic diversity on selected attitudes of elementary school teachers by investigating the effects on teacher tolerance and optimism of exposure to 1) the usual classroom situation and 2) an inservice training program. The research was conducted as a field experiment using a pretest-posttest control group design with replication. A community with a Mexican-American minority population in the southern Bay area of California was selected, and the training program was designed to increase the teachers' understanding of the children's cultural background and to help teachers increase the children's self-esteem. Results indicated that teachers with more than one year's experience with disadvantaged children were more optimistic in their approach, and that the training program made participants more liberal in their outlook. It is recommended that new teachers should not be placed in classrooms with a large percentage of disadvantaged children. Appendixes include 1) the procedure used for formation of treatment and matched comparison groups; 2) the survey instrument; 3) the classroom observation record; (4) a cybernetic model of the educational process; 5) analysis of the association between teacher background characteristics and changes in score; amd 6) a 73-item bibliography. (MBM)