Task-based instruction (TBI) is frequently promoted as an effective teaching approach, superior to 'traditional' methods, and soundly based in theory and research. The approach is often justified by the claim that linguistic regularities are acquired through 'noticing' during communicative activity, and should therefore be addressed primarily by incidental 'focus on form' during task performance. However, this claim is based on unproved hypotheses, and there is no compelling empirical evidence for the validity of the model. Many advocates of TBI reject proactive syllabus design on doctrinaire grounds, while commonly misrepresenting 'traditional' classroom practice. While TBI may successfully develop learners' command of what is known, it is considerably less effective for the systematic teaching of new language. This is especially so where time is limited and out-of-class exposure unavailable, thus making heavily task-based programmes inappropriate for most of the world's language learners. The polarization of meaning-based and form-based instruction is unconstructive, and reflects a recurrent pattern of damaging ideological swings in language teaching theory and practice.