The objective for all three phases of this study was to make improvements to an existing measure, the Dispositional Evaluation Rubric (DER), and then establish reliability and validity of the measure, which will support schools and teacher preparation programs in measuring teacher candidates' professional dispositions. This study was designed to utilize a mixed-methods approach, employing qualitative survey results, as well as quantitative correlational and dimensionality analyses. Potentially, this instrument could contribute to the enhancement of teaching evaluation systems and teaching effectiveness for both pre-service and in-service teachers. The study findings underscore the significance of the need for the development and utilization of effective rating instruments for teacher candidates' and teachers' professional dispositions. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]