This study presents an 18-month longitudinal investigation (2024–2025) of social media's educational integration among 487 higher education students in Ballari District, Karnataka. Combining quantitative surveys (N=412) with qualitative interviews (N=75), we employ an extended Technology Acceptance Model to analyze platform efficacy, behavioral patterns, and learning outcomes. Key findings reveal WhatsApp as the dominant educational platform (84.3% adoption), with students demonstrating 12.3% higher academic performance through structured social media use (p<0.01). We introduce the Social Media Learning Efficacy Index (SMLEI), showing strong correlations between platform features and conceptual understanding (r=0.68). The study provides actionable frameworks for optimizing digital pedagogy in semi-urban contexts.