Written corrective feedback (WCF) has been a long time practice in L2 writing instruction. However, in many cases, the effects are not satisfactory. There have been controversies about it both theoretically and empirically. This paper reports a multi-case study exploring individual differences that impact learners’ responses to WCF. Four students’ compositions in an English course with writing components were examined. Then, the students were interviewed. The results of analyses reveal, though all the four students were motivated to study by a compulsory provincial English test, students of significantly lower proficiency were motivated to significantly more independent learning activities after class. As a result, they achieved significantly greater improvement. It is also revealed that WCF did not lead to simplified writing in terms of lexical diversity and structural complexity, for the students knew the grading criteria for the written task in the compulsory test. Moreover, this study shows that Ferris (1999) classification of treatable and untreatable errors should be used with reference to the students’ present zone of proximal development (ZPD). Finally, pedagogical suggestions are provided.