The Conservative Dual Criteria (CDC) method is known to improve decision-making accuracy in users when interpreting graphed data. The effectiveness of this method with in-service special education teachers, however, has not been investigated. The present study examined the effects of a virtual training package designed to improve the data-based decision-making skills of in-service special education teachers. Specifically, the virtual training consisted of a training video on the CDC method, access to a decision-making guide, and a brief training assessment. Five in-service special education teachers received training in the CDC method via the online learning management system, Canvas. A multiple baseline design across participants was used to evaluate the efficacy of the virtual training on decision-making accuracy of graphed data. Results demonstrated that all participants made marked improvements in decision-making accuracy after receiving the training. Also, every participant perceived the virtual training and the CDC method as socially acceptable activities. The implications of these findings for training and future research on the CDC method with special education teachers are discussed. [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.]