VISOLE (Virtual Interactive Student-Oriented Environment) is a teacher-facilitated pedagogical approach to integrating constructivist online game-based learning into formal curriculum teaching in school education. This paper reports a case study on the implementation of VISOLE in secondary Geography education. We compared the pedagogical effectiveness of VISOLE and the traditional classroom teaching approach, in terms of students' knowledge acquisition with respect to a formal curriculum. One hundred and ninety-eight students from top, middle, and bottom academic-banding schools were selected and divided into three experimental groups and three control groups to participate in the research. Results showed that, in comparison with the traditional approach, VISOLE had a positive pedagogical effect on both low and moderate academic-achievement students, but not on high academic-achievement students. The findings shed light on enhancing the existing design of VISOLE, and provide researchers and educators with new insights into harnessing online games in formal school education in practice.