An exploration of use and believed effectiveness of interventions as well as personal interest and perceived effectiveness in working with (1) students with average IQs and depression, (2) students with mental retardation, and (3) students with both mental retardation and depression was conducted via a nationwide survey of 131 school psychologists. Results indicated that a wider range of interventions were used more frequently for students with only depression and that amount of training had significant relationships with both use and believed effectiveness of many interventions with this population. Training also was significantly related to use of interventions for students with mental retardation both with and without depression but less so regarding believed effectiveness of interventions for these students. Additional analyses indicated that number of students served with mental retardation significantly predicted interest in working with this population but that amount of training experiences regarding depression or mental retardation with depression significantly predicted interest in those two groups of students. Highest degree earned also significantly predicted interest in working with students with only depression. Amount of training in each of the respective areas was the only significant predictor of perceived effectiveness in working with each of the three groups of students. Conclusions noted the significant impact of specific training, including both direct and indirect experiences, on school psychologists' confidence when working with lower incidence populations. Recommendations regarding the implementation of more comprehensive training experiences were made; these included the practice of interventions in a simulated format for low incidence populations, the extension of application of interventions to student with mental retardation, and a focus of practicum and internship experiences based on diagnosis rather than school. Limitations of the study and recommendations for future research also were explored. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]