Story-based learning (SBL) leverages narratives to scaffold second language acquisition (SLA) by embedding linguistic forms, discourse patterns, and cultural pragmatics within meaningful, emotionally engaging contexts. This article presents a mixed-methods investigation into the effectiveness of SBL across diverse learner populations and instructional settings. The study examines (a) lexical development, syntactic complexity, and pragmatic accuracy; (b) listening, speaking, reading, and writing proficiency; (c) learner motivation, confidence, and cognitive load; and (d) instructional feasibility and scalability in higher education, language institutes, and online programs. Across two terms and multiple course contexts, results indicate that story-based learning yields significant gains in vocabulary acquisition, narrative competence, and speaking fluency, with moderate effects on writing quality and reading comprehension. The impact is moderated by factors such as story richness, cultural relevance, task design, and instructor scaffolding. The discussion situates findings within constructivist, sociocultural, and cognitive theories of SLA, and offers practical guidelines for curriculum design, assessment alignment, and scalable implementation.