This research is based on collaborative learning processes using scaffolds. Specifically, we aim to ascertain whether there are any significant differences in students' results after following the same learning instructions for participating in a virtual forum in two different subjects. We also aim to analyse the mediator's role, the use of scaffolds, and if students have followed real metacognitive processes. A total of 104 university students were involved. The main findings of our study emphasise the importance of well-designed learning instructions for participating in a virtual forum, which could be applied to any subject. Moreover, students are more active in their learning process and collaborative communication if the lecturer plays an active role overseeing students' participation and guiding the construction of knowledge.