This chapter introduces the multilingual Swiss learner corpus SWIKO while also exploring effects of contextual factors on teenage learner productions in instructed foreign language settings. Corpus-based language acquisition research relies on learner language data usually elicited through a range of tasks. However, task characteristics and conditions may influence the extent to which learners can demonstrate their language competences. To tackle this challenge, careful attention was devoted to the systematic variation of parameters (eight different tasks, solved orally or by writing, in the language of schooling or one or two foreign languages, or paper- or computer-based). These are first discussed in light of the overall composition of our corpus. We then focus on the German sub-corpus, reporting findings regarding text length, lexical diversity, and cross-linguistic influence. Our analyses reveal both quantitative and qualitative differences depending on task type and modality, and show large intra- as well as interindividual variation among learners. Despite the limitation of a (currently) small oral data set, these initial findings emphasize the crucial role of contextual factors in data collection and raise concerns about the generalizability and comparability of basic-level learner productions.