Quality teaching in large classes is generally challenging to achieve. In large classes, there are fewer possibilities for students to interact with the teacher and with each other; the motivation to study decreases as does the possibility for receiving feedback during the learning process. This can result, among other things, in reduced understanding of the learning material and therefore in lower academic performance. The aim of this study is to investigate whether computer-supported collaborative learning (CSCL) can have a positive impact on aspects of quality teaching such as interaction, motivation and understanding. Two online collaborative activities were designed and implemented in a regularly scheduled course with approximately 200 undergraduate students. This study adopted a mixed method of both qualitative and quantitative analysis: data were collected from surveys, in-depth interviews, forum logs, and exam scores. The results show that CSCL facilitates motivation, interaction and achievement of deep understanding. More particularly, one CSCL activity was found to be a significant contributor to students' academic performance and this confirmed that traditional lecturing blended with CSCL improves the quality of the teaching compared to traditional lecturing only, at least as far as understanding is concerned. Moreover, the study indicates that different types of collaborative activities have different effects on learning and that the design of collaborative activities is therefore critical to outcomes. In this respect, it also reveals that social loafing, which is usually considered to have only negative effects on collaboration, can instead have a positive impact on learning if the task is appropriately designed.