Educational technology has the potential to be transformative in secondary mathematics classrooms. Recent events have further necessitated a paradigm shift in how technology is used. In this mixed methods action research study, I study the inputs to effective technology use and establish a combined model that shows their interaction with each other towards the output of effective technology use. I then explored professional development as a treatment designed to target and increase these inputs in teacher practice. The results indicate that focused PD was effective in increasing both teacher TPACK and self-efficacy with respect to technology. Further, the majority of teachers used technology at the levels of modification and redefinition on the SAMR (Substitution, Augmentation, Modification, Redefinition) scale. Findings support the use of focused PD as an intervention. [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.]