Higher education is increasingly realized by net-based scenarios often incorporating collaborative activities. This is accompanied with specific benefits but also constraints. In computer-mediated peer-tutoring for example it is more difficult to construct mutual models, thus impairing collaborators grounding, audience design and coordination. In this paper 'Knowledge Mirroring', that is providing information about the partner's knowledge, is introduced as technological support developed to compensate for these problems. Effects of Knowledge Mirroring on audience design and knowledge acquisition are studied in a simulated peer-tutoring scenario with explaining as basic activity. Analysis of explanations revealed audience design with respect to usage of elaborations and references. Results regarding knowledge acquisition show that learners provided with Knowledge Mirroring were able to draw more inferences on information distributed across the learning material.