---

Self-assessment and peer-assessment are two means of realizing the goals of educational assessment and learner-centered education. Although there are many arguments in favor of their educational benefits, they have not become common practices in educational settings. This is mainly due to the fact that teachers do not trust the pedagogical values and the reliability of learners’ self- and peer-assessment. With regard to these points, this study aimed at investigating the effect of doing self- and peer-assessments over time on the paragraph writing performance and the self- and peer-rating accuracy of a sample of Iranian English-major students. To do so, eleven paragraphs during eleven sessions were written and then self- or peer-rated by the students in two experimental groups. The findings indicated that self-and peer-assessment are indeed effective in improving not only the writing performance of the students but also their rating accuracy. After comparing the effects of self- and peer-assessment on the writing performance and the rating accuracy of the participants, peer-assessment, however, turned out to be more effective in improving the writing performance of the students than self-assessment. In addition, neither of the assessment methods outdid the other in improving the rating accuracy of the students.