Despite the widespread use of Social Learning Networks (SLNs), there is little research on the effectiveness of these sites in related literature. Therefore, there is a need for studies investigating but use of SLNs in educational environments and their effects on learners' academic achievements. In this study, the purpose was to investigate the effects of use of Edmodo, a leading SLN site, on students' performances and attitudes towards online learning according to certain variables. In line with this purpose, using the pretest-posttest method, an experimental study with a control group was carried out with 79 learners taking the courses of Special Teaching Methods in the department of Computer Education and Instructional Technologies in the Education Faculty of a university in Turkey. In addition to face-to-face courses given to the experimental group students, various activities related to the course (group works, individual assignments, discussions) were carried out under the guidance of the course teacher via Edmodo. As for the control group students, they carried out the activities in class environment without using Edmodo. The results revealed that students who used Edmodo were more successful than those who did not. Based on this result, it could be stated that Edmodo had positive contributions to learners' academic achievements.