This study investigated the impact of a designed web-based learning module on Year 12 students' learning of argumentative writing. The module known as WebQuest Learning Module or WebQLM comprises four units of learning. The subjects were 68 Year 12 Arts Stream students in an urban school in Penang. The main objective of this study was to investigate the effect of WebQLM on students' performance in argumentative writing as well as students' responses towards the integration of this web technology in the ESL classroom. The paired-samples T-Test revealed significant improvement in students' argumentative writing performance. Findings from the questionnaire and group interviews showed students generally responded positively towards the use of WebQLM in argumentative writing instruction. This study has brought to light the importance of integrating web-based learning tasks in the classroom. The credibility of the teacher in web-based instruction depends very much on the roles he or she plays in designing, scaffolding, facilitating and aspiring students towards a better learning culture. Implications on the teaching and learning of writing in an ESL context, especially for learners in the contemporary digital culture, can be drawn from the findings.