Background: The implementation of the nine-year integrated curriculum in the primary and secondary schools of Taiwan represented, in practice, a great change to the nature of school teaching. This was mainly due to the fact that the new scheme for the curriculum required teachers to collaborate with one another, when they had been teaching students independently for most of their teaching career. Purpose: The purpose of this research was to study the effects of team teaching upon two 8th-grade teachers in the field of mathematics. The specific research question was student performance and teacher perceptions concerning team teaching. Programme description: Team teaching involves two or more teachers whose primary concern is the sharing of teaching experiences in the classroom, and co-generative dialoguing with each other. They take collective responsibility for maximizing learning to teach, or becoming better at teaching, while providing enhanced opportunities for their students to learn. Sample: The subjects of this experiment were chosen from the 8th-graders of a secondary school in Taoyuan County, Taiwan. Two certified math teachers and four classes participated in this study. One each of the teachers' two classes was selected to be the experimental group (63 pupils), and the remaining two classes (61 pupils) were the control group. The students' original placement was performed by the school according to a normal "S" distribution. Design and methods: The researcher made use of a quasi-experimental method, assigning the four sampled classes to experimental group and control group. This study was a two-stage team teaching experiment, dividing the 12-week period into two equal halves. The main research method was a combination of quantitative and qualitative analysis. The research data included student scores, questionnaires, teachers' self-reflection, video taped records of teaching performances and the researcher's interviews with teachers. Results: The research findings showed that the average final exam scores of students receiving team teaching were higher than those of students receiving traditional teaching. The two teaching methods showed significant difference in respect of students' achievement. More than half of the experimental students preferred team teaching to traditional teaching. The discrepancy between team teachers' expectations of team teaching and its implementation was apparent. The differences in the teaching strategy also exposed team teachers to challenge and being compared with each other by students in class. Besides, the team teachers had been unprepared for this comparison, especially in regard to class management. The implementation of team teaching, however, did not win the support of the school administration, which impeded teachers in holding team meetings and caused students doubts regarding team teaching. Conclusions: Since the research concentrated on a single subject, the implementation of team teaching in the field of interdisciplinary courses is needed. The key to this lies with teachers, who are required to do this actively; otherwise, educational reform will not achieve its goals. (Contains 3 tables.)