Coaching is increasingly becoming required or recommended as a form of teacher professional development, but the education field has only begun to define the practice and understand its features, especially in regard to its potential to improve math teaching in early childhood contexts. Using mixed methods and a Whole Teacher Approach theoretical framework, this study examined a math content-focused coaching model and its impact on teachers' math content knowledge, teaching practice, and dispositions including attitudes, beliefs, and confidence. Participants included 141 lead and assistant teachers and 5 coaches working in 27 Head Start centers in Chicago. Teachers at centers randomly assigned to the intervention condition participated in workshops and up to five coaching cycles consisting of planning, observation, and reflecting. Quantitative measures included: (a) the Evaluating Quality Interactions in Preschool Math video observation tool; (b) the Pedagogical Content Knowledge in Preschool Mathematics survey; (c) the Attitudes, Beliefs, and Confidence in Preschool Mathematics survey; and (d) coaching fidelity surveys. Qualitative data sources included: (a) open-ended teacher survey responses; (b) open-ended coach survey responses; (c) coaching logs; and (d) project documents. While there was no evidence of change in teaching practices in the time frame of the intervention (8 months), coaching was found to improve teachers' confidence in math teaching. This is attributed to an emphasis on planning that included role-play and attention to teachers' pedagogical content knowledge for math teaching. Results also indicate that the group coaching format with inclusion of assistant teachers increased collaboration among colleagues. [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.]