This study explores social interaction and mathematics performance, especially regarding how bilingual Latino/a students' positioning and participation evolved as they interacted with others in mathematics problem solving. Historically, Latinas/os have faced segregation in different ways that affect the quality of their social interactions and, eventually, also their learning. Although great efforts have been made in promoting equitable student participation and improving student-teacher and student-student interactions, there still remains the question of how both equitable and uneven participation evolve in natural settings. Current research has demonstrated the need to document, through longitudinal ethnographic studies, how students' interactions and social exclusion affect their learning in mathematics (Baumeister & De Walle, 2005; Zevenbergen, 2001). Thus, greater interest has evolved in children's mathematical discourses, social worlds, cooperative work (Gonzalez, Andrade, Civil, & Moll, 2001), and positional identities (Esmonde, 2009). From a sociocultural perspective, this study centered on Latina/o students and their access to resources and opportunities to learn mathematics (Gutierrez, 2008) by exploring how participation in group problem solving affected the "who you are" (positioning), and how this position affected student participation in the same event (Bloome, Carter, Christian, Otto, & Shuart-Faris, 2005). "Positioning," described as a discursive act, refers to the roles and actions that participants take up and/or are given when interacting with others (Harre, 2004). "Participation" refers to people engaging in a social activity in which the interactions, active observations, and shared thinking mediate the accomplishment of the activity, which in turn also transform the individuals (Rogoff, 1990). In essence, participation describes the engagement of individuals in a task and how they relate to one another and the task. These constructs gave rise to the following question: "How do social interactions in small-group work mediate the positioning and participation of bilingual Latina/o students during mathematics problem-solving tasks in an afterschool program?". This study drew on data gathered as part of a larger study, "Los Rayos" (Khisty, 2004), concerned with the language and cultural resources of Latinas/os in mathematics. Ethnographic data of the same students were gathered over three years in an afterschool setting. This presented the opportunity to observe circumstances and students' characteristics that in regular classrooms may be hidden or not deemed as obvious (McDermott & Varenne, 1998). The data included participant observations and analysis of 1) videotaped student interactions, 2) discourse used by participants in each group, 3) field notes developed by group facilitators (research fellows and pre-service teachers), and 4) relevant student work. I used a multiple-case design (Yin, 2009) of four students that represented contrasting cases (high or low) given their participation status observed in the afterschool and their school grades. I explored their interactions and language use affecting the evolution of their positioning and participation during problem solving. Results indicated three factors mediating the process of co-constructing one's own and others' positions, namely the quality of "attention," "alignment," and "ability" co-constructed among the participants. The quality of these factors, unevenly distributed and negotiated among the group participants, afforded different positions for participants (i.e., powerful, null, powerless, and equalized), which in turn also determined the quality of mathematical and social affordances that participants accessed in the group. Positioning patterns were flexible as all students experienced all types of positions. However, over time these patterns were recurrent and linked to specific students. Greater levels of social support were given to students with higher mathematical performance. The type of tasks and groups in which students interacted also seemed to be factors in the negotiation of positions. Codeswitching was used by bilingual participants around positioning events to mark differences or agreements, and English was used as a way to gain authority. These results as well as their implications and possible suggestions for instruction and research are discussed in the final chapter. The limitations of the study are twofold: first, the results are constrained by the circumstances of the afterschool (e.g., the study cannot make claims pertaining to a regular classroom); and second, the nature of ethnographic study, with its small number of subjects, limits the extent to which the findings can be generalized. The relevance of this study resides in the exploration of social and academic practices that support Latinos/as' positioning and participation more consistently and positively, as well as those that may limit their potential and learning opportunities in mathematics. [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.]