As an attempt to shed more light on the effectiveness of alternative assessment in second language (L2) learning, this study sought to evaluate the effect of self-assessment and peer-assessment on writing performance of Iranian English as a Foreign Language (EFL) students. To achieve this objective, a number of forty-six English major learners who were the students from two intact classes at an Islamic Azad University were employed as the participants of this study. The two classes were randomly assigned to a self-assessment group (N=22) who were trained to self-assess their writing tasks and a peer-assessment group (N=24) who were taught to assess the writings of their peers. The study intervention during which self- and peer-assessment practices were carried out for each group lasted for a period of one university semester. The required data were collected through two timed writing essays administered as the pre-test and post-test of the study. The findings revealed that both self-assessment and peer-assessment were effective in improving the writing abilities of the participants. However, it was found that the students in the peer-assessment group outperformed those in the self-assessment group in terms of writing performance, suggesting that peer-assessment was more effective than self-assessment. The discussions of the results as well as the pedagogical implications of the study were finally presented.
