While the link between teacher care and student engagement is well-established, the specific mechanisms through which this relationship operates remain undertheorized. This study employed a sequential explanatory mixed-methods design to investigate how teacher care and classroom climate foster student engagement by building academic self-efficacy in an Iranian English as a Foreign Language context. In the quantitative phase, 384 university students completed questionnaires on teacher care, classroom social climate, academic self-efficacy, and student engagement. Structural Equation Modeling was used to test a hypothesized mediation model. The results confirmed that academic self-efficacy was a powerful mediator; the positive effects of teacher care and classroom climate on student engagement were significantly explained by their capacity to first enhance students' self-beliefs. In the qualitative phase, we conducted an in-depth, multi-modal study of four purposefully selected classrooms, using interviews, digital diaries, and observations, all analyzed through a Critical Discourse Analysis lens. The qualitative findings illuminate the statistical results by revealing three key discursive practices through which teachers build efficacy and engagement: 1) a discourse of validating potential that constructs students as capable scholars; 2) the scaffolding of vulnerability through careful micropolitics of error correction; and 3) the cultivation of a collective identity through a you to we pronominal shift. Together, the findings demonstrate that teacher care is not merely an affective state but a set of tangible discursive practices that build student confidence, which in turn facilitates academic engagement.