Teachers are the key actors in guaranteeing effective teaching and learning processes. This study examined the influence of teacher collaboration on learners academic achievement in chemistry in public day ordinary secondary schools in Rwanda, Ruhango District. The specific objectives were: to determine the influence of peer coaching among teachers on learners academic achievement in chemistry, to determine the influence of team teaching on learners academic achievement in chemistry, and to determine the influence of professional dialogues among teachers on learners academic achievement in chemistry. The study will be important for the government, education policymakers, school managers, and development partners in education, among others. The study adopted a cross-sectional survey design and targeted 936 individuals including 57 headteachers, 57 deputy headteachers, and 822 teachers from selected schools in Ruhango district. A sample size of 281 respondents was selected using simple random sampling to choose teachers. Headteachers and deputy headteachers were selected using purposive sampling. Data was collected using questionnaires for teachers and interviews for headteachers and deputy headteachers. The collected data were edited, coded, and entered into IBM SPSS Version 26 for analysis. Descriptive statistical tools such as mean, frequency, and percentages were computed while inferential statistics involved correlation analysis. Pearson correlation coefficient and beta coefficients were calculated. The findings were presented in tables. The research findings proved that teacher collaboration affects learners achievement in chemistry. The research findings show teachers engage in team teaching (55.9%), peer coaching (54.4%), and professional dialogue (50.7%). Respondents notably confirmed that students performance in chemistry had improved in chemistry assessments due to collaborative teaching strategies (52.4). Findings confirm a strong positive correlation ranging from 0.77 to 0.846 between teacher collaboration and learners achievement in Chemistry. This suggests that as teachers collaborate more effectively through methods like team teaching, peer coaching, and professional dialogue, students academic performance in Chemistry improves significantly. Therefore, the researcher concludes that structured and frequent collaboration among teachers is a key factor in boosting student achievement in science subjects. Schools that prioritize teacher collaboration can expect better syllabus coverage, improved student engagement, and higher completion rates in Chemistry. In light of these findings, regular, targeted workshops, seminars, and peer coaching sessions should be organized to provide teachers with both the theoretical knowledge and practical skills necessary for effective collaboration. Such professional development activities would allow teachers to exchange best practices, develop new teaching strategies, and support each other in creating a more engaging learning environment for students. Further research could be done on the effect of teacher collaboration on learner Engagement, longitudinal study on the impact of teacher collaboration on learners Achievement in secondary schools, and the role of teacher collaboration in enhancing learners achievement across different subjects in secondary education.