Online discussions provide an opportunity for collaborative construction of meaning through peer to peer dialogue. The aim of this study is to develop an understanding of cognitive load as a factor supporting or inhibiting students’ participation in online asynchronous discussions. We employ cognitive load theory as a theoretical perspective, applying it not only to participants’ cognitive load but also to their collaboration load. Through an experimental study, we confirm that anchoring discussion leads to more task-oriented communication and less need for social and planning comments, which leaves more time and effort for the creation of elaboration and evaluation of ideas. Furthermore, anchoring discussion leads to more efficient communication as it reduces cognitive load involved in correctly interpreting messages.