This paper reports a study employing stimulated recall protocols to investigate how L1 English-speaking learners of L2 German use their metalinguistic knowledge during the resolution of selected form-focused tasks. Verbal report data from 10 university level learners were analysed to gain insight into explicit knowledge in action during controlled processing. A fine-grained analysis allowed for the characterisation of qualitative differences in learners' reported implementations of metalinguistic knowledge during task performance and the identification of variables associated with such implementations. First, reported use of metalinguistic knowledge at different levels of complexity was in evidence. Second, co-occurrences of learners' reported use of metalinguistic knowledge with success and consistency in item resolution and with different kinds of decision-making were identified. In sum, the observed behaviour patterns suggest that metalinguistic knowledge may be a double-edged sword: while the use of such knowledge seems to be beneficial in some circumstances, it is apparently not necessarily a safeguard against inconsistent and unsuccessful task performance.