This study aims to explore how high school students collaboratively solve problems in a web problem-based learning (WPBL) system in an 8-week digital logic course using discourse analysis. Employing in-depth interviews, this study also investigated the students' attitudes toward the WPBL system. The number of teaching assistants' responses had a negative relationship with the number of peer responses. Regarding dialogue quality, extended questions and brainstorming stimulated each other. Elaboration facilitated problem solving, whereas organizing knowledge from books or websites decreased reflection. Students affirmed the usefulness and effectiveness of the web system because it created an interactive, flexible, comfortable and collaborative learning environment. (Contains 4 tables and 1 figure.)