This article describes a study into the functions of code-switching in EFL classes at a Colombian language school. It was undertaken to decide whether the official "English-only" policy in place in this and other classrooms is pedagogically justified. The results suggest that code-switching may not necessarily be connected to ability level and serves multiple communicative and learning purposes. This indicates not only that total proscription of L1 is ill-advised, but that the mother tongue can be usefully exploited for learning, for example when performing contrastive analysis. However, factors including learners' expectations, the positive motivational effects of learning L2 strategies for dealing with communication breakdowns, the importance of exposure to and practice of the target code, and the need to prepare learners for L2-only contexts call for a common-sense approach where exploitation of L1 is counterbalanced with efforts to teach communicative functions in L2, and some strategies are suggested for achieving this.