This study investigates the impact of transformational leadership by school administrators on school effectiveness in Wang Chao District, Tak Province, Thailand. In semi-rural Thai schools, challenges related to digital transformation, policy decentralization, and diverse learner needs have made leadership effectiveness crucial for organizational performance and sustainability. A quantitative research design was used, collecting data from 343 administrators, teachers, and educational personnel across 13 public schools under the Office of the Tak Primary Educational Service Area 1. Standardized questionnaires measured transformational leadership behaviors idealized influence, inspirational motivation, intellectual stimulation, and individualized consideration and school effectiveness, including academic achievement, organizational development, problem-solving capacity, and teacher engagement. Descriptive statistics, Pearson product–moment correlation, and regression analysis were applied. Results show that administrators demonstrated high levels of transformational leadership across all dimensions. Transformational leadership was strongly and positively correlated with overall school effectiveness (r = .857, p < .05). Among the leadership dimensions, individualized consideration was the most significant predictor of school effectiveness, surpassing idealized influence, inspirational motivation, and intellectual stimulation. This finding emphasizes the importance of empathy, fairness, recognition, and personalized support in improving institutional performance. The prominence of individualized consideration reflects the Thai sociocultural context, where collectivism, social harmony, and mutual respect shape perceptions of effective leadership. This study provides culturally grounded empirical evidence on transformational leadership in rural Thai schools. The findings suggest that leadership development and policy initiatives should prioritize relational and human-centered competencies alongside strategic and instructional leadership to enhance school effectiveness in similar educational contexts.