Adolescent newcomer students bring a wealth of linguistic and cultural resources to their learning environments—resources that become even more dynamic when combined with those of their peers. While a significant body of research has explored students’ deployment of multilingual resources through translanguaging, most of this work does not address other semiotic resources. Multimodality literature, meanwhile, has largely ignored multilingualism. Drawing on Leo van Lier’s ecological notion of affordances, this dissertation contributes to this gap by examining the range of semiotic resources that acted as affordances for additional language development as students supported one another in negotiating classroom tasks. This study was conducted in four classrooms for newcomer students within two school sites in California: Sycamore High School and Cedar International High School. At both schools, data were collected in one classroom focused primarily on English language and literacy development (ELD and reading), and one on content (ethnic studies and biology). Methodologically, the study included participant observation, semi-structured interviews with four teachers and 12 focal students, collection of classroom artifacts, and videorecording of focal students’ interactions. Data analysis revealed a contrast in pedagogical approaches, which contributed to far more opportunities for peer interaction among students in the classrooms Cedar International than Sycamore High. Microanalysis of select peer interactions revealed that affordances for language development included oral and written features of English and Spanish, iconic and deictic gestures, and mutual engagement with material artifacts. Students skillfully pooled semiotic resources by combining their own linguistic, cultural, and content expertise with that of their classmates and material resources in the environment to negotiate the task at hand and ensure that their peers could participate meaningfully. The study suggests the need for expanding translanguaging research to consider semiotic resources other than oral and written language that contribute to language development, challenging notions of fixed expertise in peer interaction, and examining peer interaction across a variety of participant structures. With regard to classroom practice, findings point to the value of affordances for illuminating what students are capable of doing, and to the importance of expanding opportunities for students to engage agentively through meaningful collaboration.