This study investigated the effects of two independent variables including Discourse Markers’ (DMs) instruction as well as teacher and peers’ corrections on the Iranian intermediate EFL learners’ writing scores. The participants of the study were 60 EFL male learners. To examine the impacts of explicit instruction of DMs, the participants were divided into two groups of 30. One of the researchers as the EFL teacher taught the key DMs including consequences, reasons, additions and contrastives to the experimental group, while no DMs were taught to the control group. Independent sample t-test results showed a significant difference in EFL learners’ post-test writing scores in two groups. In fact, the experimental group (M = 2.40, SD = 4.35) outperformed the control group (M = 0.47, SD = 1.70) due to DMs’ use. Also an independent sample t-test was applied to compare the teacher’s and peers’ ratings in 3 writing tasks. These writings were scored analytically according to Jacobs et al. (1981) scale. The results showed a significant difference between two groups’ ratings; peers had given higher ratings (M = 85.63, SD = 10) than what the teacher had given (M = 80.71, SD = 7.97). The conclusions of this study revealed that: 1) cooperative learning activities could improve the writing skills in EFL classes, and 2) All of the components of an acceptable piece of writing, that is, content, organization, vocabulary, language use, and mechanics could be enhanced through cooperative learning activities. The implications and suggestions for further research were also formulated.