This study scrutinized the impact of Web 2.0 on the language achievement and self-regulated learning of Iranian EFL learners in online language courses. A mixed-methods approach was employed to leverage the Learning Management System (LMS) alongside WhatsApp as a supplementary tool in the experimental group. In the quantitative segment conducted over a three-month semester, an experimental design was implemented involving 24 Iranian male and female students from the Iran Language Institute (ILI). These participants were divided into two coeducational online classes: LMS and WhatsApp were utilized in the experimental group (n=12), while the control group (n=12) solely employed LMS. Quantitative data were gathered using the Oxford Placement Test (OPT), the Language Learning Self-Regulated Scale, and pre-test and post-test assessments. Concurrently, the qualitative phase entailed interviews with 8 participants, aimed at capturing nuanced insights into the advantages and disadvantages of utilizing WhatsApp alongside LMS for online learning. The quantitative outcomes revealed a notable impact on language achievement and self-regulated learning among EFL learners in the experimental group, emphasizing WhatsApp's supplementary role. Furthermore, qualitative findings shed light on the multifaceted aspects of employing WhatsApp in conjunction with LMS, unveiling both its merits and drawbacks. The implications for online EFL classes are substantial, offering valuable insights into optimizing digital platforms for enhanced language learning experiences.
