Through the evolution and proliferation of the Internet, distance and online education have become more prevalent in modern society. Synchronous web-based professional development continues to gain popularity. Although online education has grown in popularity and breadth, there has been a lack of research about the impact of synchronous web-based professional development. By using Kirkpatrick and Kirkpatrick's (2006) Four Levels of Evaluation, this study examined the impact of webinar professional development at a National Science Foundation Advanced Technology Center. Findings indicate that although the factors that contribute to learning in a web-based environment were present, there was a lack of evidence about the actual outcomes of participation in a synchronous web-based professional development. To address the lack of evidence, a new model of Comprehensive Synchronous Web-based Professional Development evaluation and implementation is proposed in the discussion. [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.]