A professional development program (PSPD) was implemented to improve in-service secondary mathematics teachers' content knowledge, pedagogical knowledge, and self-efficacy in teaching secondary school statistics and probability. Participants generated a teaching resource website at the conclusion of the PSPD program. Participants' content knowledge change and self-efficacy change were measured. After PSPD, three participants were selected to represent three types of change. Teachers' classroom instructions were video-taped and analyzed to explore the enactment of PSPD components, such as activities and concepts. Interviews were conducted to assess factors that facilitated teachers' change and the enactment of PSPD components. Preservice teachers who majored in secondary mathematics education were asked to evaluate the teaching resource website that PSPD participants generated. Their applications of content in this website and feedback to this website were analyzed. Case study research method was adopted in this study. Findings revealed that PSPD participants' self-efficacy in teaching statistics and probability improved significantly. There was a moderate positive relationship between in-service teachers' statistical content knowledge and self-efficacy in teaching statistics and probability. PSPD participants' utilization of PD components may be influenced by school conditions, the characteristics of PD materials, and whether teachers perceive and accept PD content. Six out of 17 preservice teachers utilized materials in the teaching resource website in their lesson plans. Preservice teachers preferred teaching resources that were ready-to-use and easy to access. [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.]