A web-based learning system supporting the “devil’s advocate” strategy toward online communities has been developed to facilitate collaborative argumentation activities. In this study, the pedagogical basis underlying the design and the various functions embedded in the system are explained in the light of argument theory. The software alpha test in terms of the white-box test and black-box test has been executed to establish the quality of programming and logical correctness. The software beta test has been conducted to analyze to what extent the system meets the users’ demand. Participants of this beta test are external consultants who are experienced with argumentation and computer education and external students who belong to the target user of this software. A preliminary study involving 100 sixth-grade students to evaluate the usability and the instructional potential of the system has been conducted. Results taken from questionnaires revealed that students are favorable to the system’s interface design and potentials in promoting their argumentative capability in the applied content domain. Data analysis further indicated that students feel the system has fluent navigation but appeal relative low affect to learn. Guidelines pertaining to instructional implementation are offered.