In such a rapidly developing world, it has been inevitable to integrate some modern assessment approaches and tools into English teaching. Hence, several up to date Formative Assessment Tools have been used by teachers during the learning process to modify teaching and learning activities by means of acquiring qualitative feedback. Blogs or Blogging is one of these formative assessment tools which are on focus. The aim of this exploratory case study is to find out whether or not writing blogs does have an effect on high school students' writing skills. The findings suggest that the blog is an effective tool for students to improve their English writing skills. Besides it was observed that blogging enhanced the students' eagerness to write and fostered the autonomous writing. This study also implies that writing blogs is of a great value for English learners, language instructors, material developers and curriculum designers as well as having the potential for further research.