The purpose of this study was to examine the effects of teacher–student negotiated interaction (TSNI) on grade 10 EFL students‟ grammar competence, the retention of the grammar competence, the students‟ classroom participation, and their perceptions about the approach to learning grammar. The study used a quasi-experimental design and a mixed-methods research approach. The investigation focused on past tenses and passive voice. TSNI was implemented in the experimental group to teach grammar. The comparison group received conventional (teacher-led) grammar instruction without collaborative dialogue with the teacher. The intervention lasted for eight weeks. Data were collected through tests, questionnaires, semi- structured interviews, and classroom observation. Independent samples t-tests, one-way repeated measures ANOVA, one-sample t-tests, and descriptive statistics were employed to analyze the quantitative data. Thematic analysis and classroom discourse analysis were used to analyze and interpret the qualitative data. In the past tenses, the experimental group showed a mean score of 64.83 in the posttest, while the comparison group scored 50.07. The independent samples t-test (t = 14.875, p < 0.05) confirmed a statistically significant difference between the two groups. Likewise, in the posttest results of passive voice, the experimental group scored 66.31, while the comparison group scored 53.32. This study suggested that TSNI is more effective than conventional (teacher-led) grammar instruction in improving students‟ past tense and passive voice competence. In addition, the findings revealed that the overall frequency of students‟ participation in grammar classes showed a significant increase over time. The results also indicated that TSNI interaction could lead to sustained grammar competence across time. Furthermore, data from questionnaires and semi-structured interviews showed that experimental group participants had positive perceptions about teacher–students negotiated interaction in grammar classes. Based on the findings, it is recommended that TSNI be adopted in EFL classrooms to teach grammar and boost students‟ classroom participation.