Early childhood experiences set the foundations for health, well-being, and learning; quality interactions at this stage of development improve outcomes for young children. Teacher qualifications, training, and professional development (PD) are important components of best practice in early childhood education (ECE) and are frequently used as indicators of program quality as they are believed to improve teacher skills in the classroom. Research on the effectiveness of PD yield mixed results, often indicating that the intensity (dosage) and type of training may matter more than teacher qualifications in improving teacher practice, specifically with teacher-student interactions in the classroom. However, most studies with modest effects of training on improved classroom interactions have been conducted among preschool teachers of publicly funded schools and centers. Furthermore, not much is known about how teachers' beliefs and perceptions influence transfer of learning from PD into their teaching practice. This mixed methods research examines the relationship of training dosage on classroom interactions of teachers for children from birth-5 years old in non-publicly funded ECE centers. It also explores the beliefs and perceptions of teachers about best practice in ECE and how that influences application of training into classroom practice. [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.]