Teacher feedback on EFL students’ writing is essential in the teaching and learning process. While a large body of research has focused on treatment of errors and content feedback in general, little has been done about the types of mistakes that students can overcome by themselves and how comments on contents should be worded. There are two major causes of errors: first language interference and developmental factors. The former type is harder for learners to overcome and the latter category can be gradually improved by their own efforts. This paper serves dual purposes: diagnosis and treatment. First, it examines types of errors that could be fixed by students with teacher’s assistance. Second, it looks into how content feedback should be worded. It specifically analyzes marginal and final comments broken into five categories to see how these types of content feedback help students improve their rewrites. It was found that errors with subject-verb agreement and with nouns used for generic references belong to developmental errors and, thus they do not need teacher’s intervention; teacher’s comments with directions/suggestions and questions for clarification are the most effective for students to improve their rewrites.