This article provides a cultural-historical (CHAT) analysis of the practices used by an effective teacher of Latino/a children previously classified as "underachieving" and "beginning/novice" English Language Learners. Although the teacher would not describe her practices in strict CHAT, or sociocultural theory (SCT) terms, our analysis shows that teaching practices in this classroom are better understood using a SCT model rather than more prevalent second language acquisition (SLA) models that dominate the field of bilingual/English as a Second Language education. We describe the fundamental limitations of SLA assumptions about learners vis-a-vis a SCT perspective and use classroom and case study data to illustrate how a CHAT perspective illuminates this teacher's practices. From a CHAT perspective, teaching and learning are socially reorganized around the mediation of dynamic learner identities and include shifts in expert-novice status, dialogic interactions, and the use of innovative mediational tools (e.g., keystrokes on a calculator) to promote academic writing and oral communication. The mediational reorganization described in the classroom opened up access to students who might have been dismissed by a SLA model as "incapable" of engaging in such tasks. We draw on classroom-level data (i.e., standardized scores in reading and math) as well as the work of selected focal students to illustrate our case. (Contains 1 footnote, 2 tables, and 6 figures.)