Debriefing is a key component of simulation that promotes development of students' reflective processes. Instructor-led debriefing (ILD) is considered the gold standard; however, research conducted over the past decade demonstrates the negative effects of anxiety on student reflection during ILD. Nursing students' experiences with ILDs have been substantially investigated; yet scant research explores students' perceptions and experiences of more learner-centered debriefing formats that deemphasize the instructor role. The purpose of this grounded theory study was to explore undergraduate nursing students' perceptions and experiences of a hybrid debriefing format consisting of peer-led debriefing followed immediately by ILD. Specifically, I aimed to inductively develop a theory grounded in the student experience to provide understanding of the actions and social processes that occurred as students engaged in the combined debriefing format. I also sought to better understand how associated social processes affect reflection during debriefing. Straussian grounded theory informed all aspects of the study's research plan, sampling techniques, and data collection and analysis. I conducted the study at a public university in Anchorage, Alaska. I used purposive sampling to identify an initial cohort of senior-level nursing students enrolled in specific associate or bachelor's degree nursing courses who possessed first-hand experience with the hybrid format. Thirty-four nursing students participated in the study. Data were collected over 6 months during semistructured focus group interviews (2-6 participants per group) conducted separately by program. Focus group interviews were recorded and transcribed. A demographic survey, completed by the participants, described the sample. Field notes, observational notes, and memos provided supplemental secondary data. The core category that explicated the pervasive, fundamental patterned processes that emerged from the data analysis was "fluctuating cohesion." "Fluctuating cohesion" involved students' predominant sense of experiencing multiple transitions between states of collective unity ("we-ness") and individual separatism ("me-ness") as they progressed through the two-part debriefing format. The dichotomy between the informal collaborative environment of peer-led debriefing and the instructor-driven nature of ILD resulted in fluctuations in group cohesion. The multifaceted process of "fluctuating cohesion" was comprised of five related categories: "discovering the process," "normalizing experiences," "developing mutuality," "dynamic balancing," and "engaging informal social connections." "Discovering the process" involved the individual and collective actions of students upon encountering a debriefing format that challenged the existing paradigm. "Normalizing experiences" encompassed students' actions aimed at simultaneously diffusing emotions and seeking validation and empathy. Through the process of "developing mutuality," students' evolving sense of interdependence fostered a sense of empowerment and collective unity. The process of "dynamic balancing" involved students responding to the demands and incongruencies experienced upon encountering the shift from a self-directed to an instructor-directed debriefing agenda. Lastly, by "engaging informal social connections," students turned to trusted relationships to retain a sense of togetherness, to continue emotional processing, and to extend reflection in self-selected, nonthreatening settings. The study findings indicated that augmenting ILD with peer-led debriefing promoted psychological safety, facilitated the development of team behaviors, and enhanced reflective thinking after simulation. The study findings provided a theory-based foundation for future research and practice, including instrument development and educational strategies to optimize debriefing effectiveness. [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.]