Guided by symbolic interactionism and cultural historical activity theory this study investigated how four bilingual Latina/o pre-service teachers use language (Spanish and English) and culture, defined as social practices, as instructional resources in mathematics. The setting of the study was an after-school bilingual mathematics program, namely "Los Rayos de CEMELA" where pre-service teachers worked on mathematical activities with small groups of bilingual Latina/o fifth-grade students. The main research question underlying the study was: How do bilingual Latina/o pre-service teachers use language and culture as resources for assisting Latina/o students in mathematics. Sub-questions included: (1) How do these pre-service teachers use English and Spanish to mediate students' engagement in mathematical activities? (2) How do these pre-service teachers utilize their own and students' shared experiences (cultural knowledge) to mediate students' engagement in mathematical activities? To answer these questions, I used ethnographic methods and collected data of the pre-service teachers' nine-week participation as mathematics facilitators in "Los Rayos de CEMELA." The sources of data for the study included observations of the pre-service teachers' interactions with 5th grade students in "Los Rayos," their oral comments during weekly debriefing meetings, and their written comments in their field-notes. I utilized a grounded theory approach to analyzing the data and found that three key factors--group members' language choice and behavior, the nature of the mathematical activities, and the pre-service teachers' experiences as bilingual mathematics learners--influenced language and culture as resources while facilitating mathematical activities in Los Rayos. These findings suggest that pre-service teachers' use of language and culture as resources reflect the social definitions of Spanish and English that permeate our society. They also reflect the pre-service teachers' cultural models for teaching and learning mathematics and for community-based activities. Implications for the mathematics teacher preparation of Latina/o teacher candidates are discussed. [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.]