The topic of research is “Teacher training and academic performance of secondary schools in Rwanda” a case study of Nyagatare District. The purpose of this study was to establish the relationship between teacher training and academic performance of secondary schools in Nyagatare District. The problem at hand was that in order to improve performance of secondary schools, the Government of Rwanda (GoR) through Ministry of education and development partners adopted various initiatives to promote teacher professional development such as Rwanda English in Action Program (REAP), School Managers Training, Distance Learning and In-service Training Initiatives like Strengthening Mathematics and Science Education (SMASE), but there was little evidence to show that secondary teacher training had improved the performance of secondary schools in Nyagatare District, and thus this paper was written to investigate whether teacher training improved academic performance of secondary schools in Nyagatare District. The researcher used purposive sampling and simple random sampling to select respondents that conform to the realization of objectives of the study. The respondents were education leaders, teachers and students of schools in Nyagatare District. To collect primary data, well-structured questionnaires were employed on 134 respondents who included teachers and students whereas interviews were employed on 13 education leaders from Nyagatare district. The findings of the study show that teacher training improved the quality of teachers by helping teachers improve their qualification, skills in preparing pedagogical documents, improved teaching methods and teacher confidence in handling different situations and the relationship between teacher training and academic performance was established by improved students’ grades every year, improved students’ class attendance and participation and teachers’ improved teaching methods. The researcher concluded that teacher training played a significant role on academic performance of secondary schools in Nyagatare district by improving teachers’ competence and availing room good learning atmosphere and gave recommendation of training all un qualified teachers in all schools and to improve teacher remuneration and motivation so as to attract teachers to the teaching profession.