The purposes of this study are to examine what type of errors students make more between form-based and meaning-based errors, as well as to investigate in which error categories Korean learners frequently make errors and mistakes. In three studies, 264 essays from 42 subjects who were at a Korean university were collected. This study adopted error correction symbols by Harmer (2007) to analyze error categories simply and easily. The results indicated that form-based errors (91%) were generally reported much more than meaning-based errors (9%) by both the teacher's and students' review. In contrast, although students had different situations in three studies (e.g., a case study, two sample studies), the results were not much different: learners frequently made errors with "the article" and "grammar" categories. In English as foreign language (EFL) environments, interactions via peer-review feedback have been considered as profitable tools; however, teacher-review feedback is still required to facilitate students' second/foreign language (L2) development. These findings suggest that students will develop the quality as well as the accuracy of their writing when they recognize the most frequent error categories in their L2 writing. (Contains 4 figures, 11 tables, and 5 footnotes.)