This study examined the types of teacher reflections and the changes in reflective levels as 15 candidates for National Board Certification worked through the portfolio process. This study also examined how the portfolio requirements and mentoring from candidate support providers helped teachers deepen their levels of reflection. Study findings determined a significant difference in levels of reflection between the first National Board portfolio entry completed and the last entry completed. When examining the mechanisms behind this growth, it appeared that the structure and focus provided by the portfolio prompts, when combined with the opportunity to review one's lessons via videotape may help teachers identify a problem to reflect upon. The writing process involved in developing a portfolio entry led to sustained thinking on important instructional issues, which led to deeper and more important reflections with implications for future instruction. Candidate support providers (CSPs) or other mentors helped candidates define the problem accurately and they also furnished alternative perspectives that may bring holes in reasoning into teacher's awareness, creating a cognitive dissonance that provides impetus for changing practices. CSPs helped candidates focus on the portfolio prompts and provided emotional support required for deep and honest reflections, thus ensuring that the reflections were meaningful and the changed practices more likely to improve student achievement. [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.]