The study aims to investigate the effectiveness of WhatsApp as mediating tool to support learning of organization and mechanics in descriptive essay writing and foster online interaction. In this study, the mixed method approach was employed. The research included sixty students from three intact classes selected through convenience sampling. The investigation was based on a quasi-experimental design in which pre-test was administered to the participants in both the control and experimental cohort to determine the baseline knowledge. After the treatment, the participants sat in post-test followed by a semi-structured interview. The quantitative results of this mixed-method study revealed that students in the experimental group outperformed the participants in the control group in terms of descriptive essay writing. The qualitative findings demonstrated how WhatsApp could help students write better descriptive essays in terms of organization and mechanics. The main reason given for the results was WhatsApp's ability to foster an interactive and cooperative learning environment, which is beneficial for learning how to write descriptive essays, particularly with regard to organization and mechanics. However, several difficulties were mentioned, such as the deluge of SMS messages. Future research directions and writing pedagogy implications suggest that social media tools such as WhatsApp should be used as mediating tools to supplement the traditional pedagogy.

Index terms: Social media, WhatsApp, interaction, descriptive essay writing, organization and mechanics