This paper reports on an investigation of semiotic mechanisms mediating collaborative activity during pair/group work interaction at the computer. The study is informed by sociocultural theory. The participants were university students of L2 Spanish performing three tasks in two modes of implementation: computer vs. paper-based. The questions addressed relate to the degree and functions of repetition, L1 and reading aloud deployed during interaction in both media. The findings suggest there is a high degree of variation in the use of these semiotic tools. No significant medium-related difference was found in the degree to which these mechanisms were deployed by the participants, but a significant difference was found between the use of the three mechanisms overall. The functions for which the mechanisms were used provide some interesting insights into the nature of semiotic mediation during interaction in general and into the role of the computer in the L2 classroom, in particular. (Contains 6 tables, 4 figures, 8 notes, and 3 excerpts.)