This mixed methods action research study examined the implementation process and impact of a 9-week Number Talk intervention to build number sense in kindergarten students. Fifty-eight kindergarten students engaged in daily Number Talk lessons for 9 weeks. Qualitative data were collected to evaluate the strengths and challenges of the implementation process with the teacher participants through a twice weekly observation tool and through bi-weekly math professional learning community discussions. The qualitative data gathered were coded for themes using Tesch's Eight Steps for coding information. The data allowed me to evaluate the implementation process to determine if Number Talks were implemented with fidelity during the implementation process. Quantitative data were collected with the Number Sense Screener (NSS) assessment instrument. The students were given the NSS as a pretest before Number Talk implementation and as a posttest after the 9 weeks of implementation. A paired sample t test was utilized to analyze the pre and posttest results. The t test was completed using the results of the pre- and post-NSS, and analysis showed a significant gain in the mean score for the targeted group. The qualitative and quantitative data were utilized by the participating teachers and me to create an action plan for future Number Talk implementation within the school. The action plan includes four steps for implementation to support lesson planning, implementation reflection, implementation walk-throughs, and formative assessment of number sense. [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.]