Assuring the quality of early childhood education (ECE) settings is a fundamental consideration for supporting young children's learning and development. Head Start programs serve children and families living in poverty, highlighting the need for equitable and high-quality learning opportunities for these vulnerable populations, and the ECE workforce characteristics are foundational considerations for providing quality care and education. However, the existing literature has yielded mixed results regarding the association between teacher characteristics and classroom quality. Furthermore, the administrative staff within the ECE settings have been a relatively neglected area within inquiries into ECE quality. The current study aimed to explore Head Start teachers' and center directors' characteristics as predictors of classroom quality using data from the Head Start Family and Child Experiences Survey (FACES) 2014 data with hierarchical linear modeling (HLM) approach. The analysis sample consisted of 302 centers/directors and 692 classrooms/teachers. Selected survey questions from Core Teacher and Core Center Director surveys and classroom observation scores from the CLASS measure were used as the study variables. Regarding teachers' characteristics, level of education demonstrated negative associations with CLASS Emotional Support and Classroom Organization scores. In addition, as the teachers experienced increased coaching/mentoring support, the Classroom Organization scores decreased. With respect to center directors' characteristics, the results indicated significant moderations for the associations between teachers' professional development (PD) experiences and classroom quality scores. As the directors had higher levels of education (i.e., graduate degrees), ECE/Child Development-related degrees, higher years of experience, and more workload related to teachers, the CLASS scores were higher, despite the teachers' decreased in-service PD experiences. On the contrary, for the directors who felt more challenged regarding their managerial duties, the teachers' increased in-service PD experiences were positively associated with classroom quality scores. The overall results, along with a discussion of the implications, shed light on the potential roles of teachers' in-service PD experiences and center directors' characteristics on classroom quality across Head Start centers. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]