This study aimed to investigate the assessment techniques used by a teacher in assessing students’ writing skills, the reason in implementing the techniques, and the students’ responses toward the implementation of the techniques. The collected data in this study included classroom observation that had been held in three times, interview, and written document. The following is the conclusions based on the data analysis. Since formative assessment of writing skill is the main focus of this study, the teacher implemented five writing performance tasks suggested by Brown (2010) namely dicto-comp, picture-cued task, short answer task, guided question and answer, and paragraph construction task. From the teaching process done by the teacher, the assessment tasks were implemented for formative purposes, that is, to monitor students’ progress in comprehending the lesson that is about narrative text. The teacher implemented some assessment tasks in an informal way to monitor students’ ongoing progress without recording the result of the performance, while the other tasks were implemented in a formal way to record students’ progress and to give them an appraisal of their progress and achievement.