Abstract
Grammar error is one of the difficulties experienced by students in the writing process. The main objective in this study was to find the usual grammar mistakes made by English language students in 2017 at Padang State University in writing discussion texts. Theoretically, this research was conducted to identify, classify and show the proportion of each type of error made by students. The type of research used is qualitative research with descriptive methods. The research subjects were students of English language education at Universitas Negeri Padang, specifically students in the K.2-2017 class. The instrument used is documentation of student writing about discussion text. All grammatical errors that appear in student writing are analyzed using the Surface Strategy Taxonomy introduced by Dulay et.al. The findings showed that the total error is 260 errors. Most errors were omission (50 errrors / 50.77%), second place was misformation error (75 errors / 28.85%), third place was addition error (39 errrors / 15%), and the last was misordering error (14 error / 5.38%). Based on these results, it can be concluded that students still experience great difficulties in learning the grammar structure in the writing process.