Teachers' professional learning is regarded as one means through which to improve instruction and student achievement, but how teachers' learning experiences actually translate to improved outcomes is not clearly understood. This is particularly true for novice teachers, who, through a combination of induction programs, broader professional development initiatives, and other activities of their own pursuit, are especially likely to receive inputs into their professional learning from multiple sources simultaneously. Despite a general consensus regarding the characteristics of effective professional learning experiences, recent large-scale studies have challenged understandings of effects of theoretically promising professional learning initiatives, suggesting a need for greater attention to understanding professional learning mechanisms. Drawing on social cognitive and organizational perspectives as well as a cognitive-affective model of conceptual change, this study uses mixed methods--multiple regression with a sample of 53 first-year middle school mathematics teachers and a multiple case study of 8 of these teachers across two years--to gain insight into teachers' responses to professional learning activities as well as their schools' roles in facilitating the professional learning process. Results suggest that teachers indeed engage in a process of cognitive-affective response to their professional learning content, including an awareness of structural and conceptual inconsistencies between aspects of their jobs and key ideas from their professional learning, but that the nature of this process may be unrelated to the quality of teachers' learning experiences and inconsequential for outcome measures. Although regression analyses did not indicate a substantial role of school organizational features in teachers' learning, case studies uncovered patterns indicating that the school indeed plays a role, which primarily involves providing opportunities for teachers to engage systematically in processing their professional learning content, through a combination of structures and leadership to promote non-superficial attention to new ideas. Given the importance of effective teacher learning for the improvement of instruction and student achievement, the study contributes toward understanding why promising professional learning experiences may fail to deliver expected outcomes, in particular highlighting the connection between teachers' cognition and schools in the professional learning process. [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.]