This study explores into the effectiveness of Team-Based Learning (TBL) as a pedagogical intervention aimed at bolstering mathematical computation skills and fostering deeper conceptual understanding among ninth-grade students. Conducted at Sherubling Higher Secondary School in Bhutan, this research directly addresses a concerning and persistent decline in mathematics performance observed within this specific student demographic. TBL is conceptualized and implemented as a highly structured, collaborative pedagogical approach meticulously designed to cultivate active student engagement and significantly improve learning outcomes. The methodological framework adopted for this investigation was a sequential explanatory mixed-methods design, involving a cohort of 53 Grade Nine students. Comprehensive data collection encompassed pre- and post-intervention assessments of both conceptual understanding and computational proficiencies, alongside detailed attitude surveys and systematic classroom observations. The quantitative analysis yielded compelling evidence of TBL's positive impact, revealing a statistically significant 14% improvement in students' average mathematics scores, which rose from an initial 51% to a post-intervention 65%. This substantial gain underscores the efficacy of the TBL approach in enhancing academic performance. Furthermore, qualitative data, gathered through various observational and survey instruments, consistently indicated that TBL profoundly influenced student engagement, actively promoted collaborative learning behaviors, and fostered more positive attitudes towards mathematics. It is noteworthy, however, that a segment of the student population continued to express a preference for individual learning modalities. Collectively, these findings robustly highlight TBL's considerable potential as a valuable and transformative educational strategy, capable of not only boosting academic proficiency in mathematics but also of developing crucial 21st-century skills, such as effective teamwork, critical thinking, and problem-solving abilities.