The purpose of this study was to examine the effect that a writing teacher's written comments had on improvement in L2 writing; whether the types of changes students made in their drafts after teacher comments were substantial at the content level and/or language level; to what extent the focus (content- and language-focused) and the directness (direct and indirect) of teacher feedback predicted improvement in L2 writing; and the teacher's and students' attitudes toward and perception of good writing and the role of teacher comments. The study had three major components. First, a quantitative study was conducted to examine the rate of students' successful revisions in response to the teacher written feedback. Using descriptive statistics, it was found that students revised more successfully in response to language-focused comments and direct comments than in response to content-focused comments and indirect comments. The next phase of the study investigated how the focus and directness of teacher comments resulted in and predicted improvement in writing. Using paired sample t-tests, it was found that teacher's comments on student drafts did lead to overall improvement in the grades on the revised essays. Employing hierarchical regressions, it was also found that higher rates of successful revision in response to content-focused comments and direct comments resulted in higher grades in the subsequent revisions. Using a one-way repeated measures analysis of variance (ANOVA), it was also found that while students' writing improved significantly for new essay assignments in the area of content, there was no statistically significant improvement in students' linguistic accuracy in their writing over the course of the semester. The final part of the study examined the students' perceived need for teacher feedback and revision, and the teacher's view on writing. Using surveys and interviews, it was found that the teacher and students had different opinions about the role and importance of feedback. The students reported that direct corrections of linguistic errors were less beneficial to them, even though the teacher gave much more direct corrective feedback than indirect feedback over the course of the semester. In addition, while the students expected to have received the grades of each writing assignment, the teacher only commented on the drafts and gave out a single overall grade at the end of semester. The study, using quantitative and qualitative methods to analyze multiple sources of data, presented strong empirical evidence that the content-focused comments and direct comments provided by the teacher contributed to higher grades in the subsequent revisions of the same essay assignment, and that there was no effect of teacher comments, especially direct corrections on linguistic features, on longer-term improvement in L2 writing. These results suggest that when giving written feedback, writing teachers should take into account whether students are developmentally ready to learn the lexical and grammatical forms and structures corrected by teachers. The study, designed as longitudinal study in a real world setting, provided a rich description of the effect of a teacher's commenting practice and L2 writers' revision behaviors. / CITE/Language Arts