The purpose of this study was to develop an instrument to assess probation officers knowledge levels of offenders with intellectual disabilities by utilizing a synthesis of subject matter analysis technique and a comprehensive review of literature. This study was conducted in two phases. The first phase was devoted to establishing the knowledge domain and development of the needs assessment instrument. For this phase the available population consisted of four subject matter experts in southern Illinois and one subject matter expert (SME) from London, England. In order to develop an instrument to assess knowledge that probation officers have about offenders with ID, an establishment of knowledge domains through face-to-face interviews with subject matter experts were completed in this phase. In addition to the content analysis from SME interviews, a comprehensive review of literature on intellectual disabilities was conducted. Outcomes from both methods were compared and similar findings were combined and used to construct items for the first draft of the instrument. A pilot test for the newly developed needs assessment instrument was conducted in the second phase. In order to obtain this validation a pilot field test and re-test, a sample of 25 Jackson County, Illinois, First Circuit Probation, Western Region, juvenile and adult probation officers was used to administer assessment (developed in phase I). Approximately two weeks after first administration, the assessment was re-administered on the same sample population of probation officers. The data source was "Probation Officer Knowledge of Intellectual Disabilities Assessment" instrument test-retest scores. Responses were scored by giving correct answers one point, and incorrect answers zero. This yielded a total score for knowledge of intellectual disabilities. Scores from the first test administration was compared to scores from the second administration by reviewing overall score correlations. Once each item was computed separately, then all item-total correlations were computed. Cronbach's alpha estimate of reliability was also computed for both the first and second administrations (Trochim & Donnelly, 2007). Additional analysis performed in this study included (a) cut offs for high or low scores based on means, (b) item difficulty, (c) inter-item correlations and, (d) descriptive frequencies on items that assessed probation officers' opinions on organizational structure and attitudes about supervising offenders intellectual disabilities. The ultimate goal of this study was to establish knowledge domains and develop an instrument to assess probation officers' knowledge of offenders with intellectual disabilities. The results of the study can be used to add information to the body of literature to eventually build up enough support to determine a need for criminal justice agency administrators to incorporate effective training material on offenders with intellectual disabilities within curriculum development for new staff orientation, in-service or academy training of probation officers. [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/en-US/products/dissertations/individuals.shtml.