This mixed-methods study (100 pre-intermediate EFL learners) explored how teacher-student interactions and code-switching affect language acquisition.  Meaningful dialogue, scaffolding, and feedback boosted learning.  Code-switching, particularly for complex explanations, aided comprehension.  Positive student attitudes towards code-switching correlated with better engagement and retention.  Classroom size and teacher proficiency influenced code-switching effectiveness.  The study emphasizes the importance of balanced L1/L2 use in EFL contexts.