This case study aims to investigate the impact of English writing skills on learners' performance in secondary schools in Kicukiro District. Guided by Vygotsky’s sociocultural theory and Richards’ Communicative Language Teaching (CLT), the study used a mixed-methods approach. The study targeted 147 participants, comprising learners, teachers, and heads of studies, from which a sample of 75 participants was selected using proportionate stratified and purposive sampling techniques. Primary data was collected through both interviews and questionnaires, assessing the impact of English writing skills on learners' performance, exploring effective teaching approaches, identifying factors contributing to low English writing skills among learners at secondary schools in Rwanda, and examining the influence of teaching strategies on learners' writing skills. Out of these findings, the paper discloses that essay writing, agenda writing, playwriting, poetry writing, and minute writing skills considerably influence learners’ performance. The study suggests enhancing learners' writing skills through regular writing activities like letters and short stories. Teachers of English should also be role models for their learners when teaching to uplift their writing motivation. In a similar or different setting, future studies should investigate the relevance of other skills to primary learners.