This chapter is motivated by the fact that few studies have been made about the effects of one-on-one writing tutoring in English writing centers in Chinese universities. It intends to examine the effects through the evaluation of tutors' performance by students. A sample of 57 students responded to the questionnaires designed based on Kaplan's 7 EFL writing objectives proposed in his theory of contrastive rhetoric with minor revision, and 12 participated the structured in-depth interviews. Results demonstrate that tutors have achieved higher level of satisfaction in objectives of vocabulary and expressions (86%), sentence and grammar(85%), etc., but lower satisfaction level in those of awareness of audience(37%), discourse structure (34%), and rhetoric and writing knowledge (40%). The findings indicate no significant correlation between tutoring duration and students' improvement extent, yet a strong negative association between students' language proficiency and their improvement. Finally, some measures about enhancing tutoring effects are suggested.