With over 12 million children enrolled in early care and education programming across the U.S., families with children under the age of 5 years old are dependent on these programs. Although highly important, little regulation exists regarding qualifications necessary for individuals to work in these programs. Consequently, individuals in the field bring a plethora of professional development experiences, skills, and competencies. This variance is partly a result of the uncertainty surrounding what should be required. Major information about the impact training and education have on these programs is missing from quantitative research, including capturing content and quantity, accurate measurement of professional development, and clear and consistent definition and categorization of training and education across studies. To contribute to the advancement of accurately describing and understanding effective teachers' professional development experiences in terms of content, quantity, intensity, and duration, a descriptive-comparative design was used to explore how the professional development experiences of teachers in 10 good quality early care and education classrooms (as measured by the Early Childhood Environment Rating Scale-Revised [ECERS-R]) differed from the professional development experiences of teachers in 10 poor quality classrooms serving children ages 2 1/2 to 5 years old. Well-defined and recommended categorizations of training, education, and documentation of staff qualifications were used. Other factors that might influence instructional quality, such as program, classroom, and support staff characteristics, were examined as well. Between-group differences of 30% or more were interpreted as interesting. Numerous between-group differences emerged regarding teacher education, training, and credentials. Among these findings, teachers in the good quality cohort were more likely to have completed course content specific to early care and education, including specific combinations of coursework in conjunction with supervised practical experience. The intensity and duration of teachers' exposure to course content was also greater in this cohort. Furthermore, in describing differences, new categories and definitions emerged, including piecemeal and comprehensive education, piecemeal and comprehensive training, content clustering, solo teaching, and hierarchical structuring of staff. These findings can be used as emerging foundations for larger scale research. [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.]