Abstrak
This research aimed to investigate the effect of Grammar-Focused Writing Instruction (GFWI) on the writing ability of tenth-grade students in composing recount texts at MAN 1 Pasaman Barat. It was done at MAN 1 PASAMAN BARAT. The researcher identified several problems, including students’ difficulties in writing and grammar, as well as monotonous learning resources. In this research, the design of the research used the quantitave approach with quasi-experimental research design by using pre-test post-test experimental and control group design. The population were all tenth grade students’ of MAN 1 PASAMAN BARAT. To determine the sample the researcher used purposive sampling. The sample was X.E.1 as the experimental class and X.E.3 as the control class. The research data were collected through a writing test as the primary instrument. Furthermore, the data were analyzed using non-parametric statictical tests, specifically the Wilcoxon Signed-Rank Test and the Mann-Whitney U Test. The result of the research indicates that the students in post test was higher than the score of pre test experiment. From the data, the mean score of students pretest was 55.15, and then the mean score of students posttest was 81.67. it is means these results sugested that the Grammar-Focused Writing Instruction method significant students’ writing ability. In additionally, from the calculation of the data the Wilcoxon Signed-Rank Test for the experimental group showed a significant value of p 0.001 (Z = -5.012), indicating a significant internal effect. Furthermore, the Mann-Whitney U Test comparing both groups resulted in p 0.001, proving a significant difference. The N-Gain score for the experimental group was 0.59 (medium improvement), compared to -0.2 (low) for the control group. It can be concluded that GFWI is highly effective and provides significantly better results in improving students' writing ability compared to conventional methods.