In the last decade, with the increased attention to learner-centred curricula, the topic of self-assessment and peer assessment has become of particular interest in testing and evaluation. The present study explores the role of self-assessment, and peer assessment in promoting writing performance of language learners. To do this, 157 intermediate TEFL (Teaching English as Foreign Language) students were assigned to five different treatments in five groups: four experimental groups and one control group. The first experimental group did journal writing as a self-assessment technique, the second group self-assessed their own writings, the third group employed peer assessment, and the fourth group had both self- and peer assessment. Moreover, there was teacher assessment in all experimental groups, except the fourth group, i.e., the self- and peer assessment group. In the control group, there was only teacher assessment. Also, at the beginning and end of the semester, all participants took a writing test. The design of the study was quasi-experimental, non-randomised control group, pre-test-post-test design. The results revealed that in the second and third groups, in which the students employed self-assessment and peer assessment, together with teacher assessment, we observed the maximum improvement in writing. (Contains 16 tables.)