Peer mentorship programs have mostly emphasized formal structures, wherein a more experienced student guides a less experienced student. However, these practices are hierarchical and require substantive resources to organize and implement. Searching for alternatives, we research the effectiveness of an informal teaching technique that facilitates active learning and peer-mentorship from everyday classroom settings and processes. Drawing on formative feedback from students enrolled in a lower-level Sociology course over a term, this paper analyzes how a "Liberating Structures" (LS) technique called Five Whys (an adaptation of the Nine Whys of LS) can promote in-class collaboration, peer mentorship, and increased engagement without training and the need to design a formal peer-mentorship program. Students identified many benefits, including that Five Whys promoted community, reflective learning, and deepened engagement with course content. However, the structuring of interactions was seen to be stifling to natural group processes. Broader implications for LS and in-class mentorship are discussed. [Articles in this journal were presented at the University of Calgary Conference on Postsecondary Learning and Teaching.]