While the positive effects of peer tutoring in a face-to-face classroom are well documented, studies of computer-aided peer tutoring are less common. However, such exercises have the potential to introduce additional student–student interaction in distance, online and blended courses. Additionally, technology can provide both students and instructors with unprecedented amounts of information related to tutor competency and methods. With these ideas in mind, we have developed a web-based peer-tutoring system called Opal (Online Peer-Assisted Learning) for use in problem-based undergraduate courses. Tutoring interactions on Opal use problems as both contexts for discussion and enforcers of tutor competency—that is, each interaction is based on a single problem, and students must demonstrate competency by answering the problem correctly on a computer before they become eligible to teach it. Based on social network analysis methods and a student assessment of learning gains survey, the introduction of this method of peer tutoring has had a positive effect on student–student interaction and student learning in our course and may have broad implications for peer tutoring in courses that involve digital problem solving as a key component.