In the present study, we take a longitudinal, corpus-based perspective to investigate short-term (over 9 months) linguistic change in the language produced for the spoken and written sections of the TOEFL iBT test by a group of English-as-a-foreign-language (EFL) learners in China. The goal of the study is to identify patterns that characterize the trajectory that language learners move through in terms of their use of phrasal and clausal grammatical complexity, as mediated by mode (spoken and written) and task type (independent and integrated). Results of a multidimensional analysis reveal that in many cases, learners developed in expected ways: discourse styles at Time 1 were not always aligned with mode- and task type-specific discourse patterns but developed over time, with discourse styles at Time 2 better approximating expected norms and exhibiting increased task differentiation. These changes were particularly noteworthy for Dimension 1, which is related to phrasal and clausal complexity. Results of a developmental complexity analysis revealed more mixed results, seeming to indicate that the relatively low-proficiency learners represented by the longitudinal corpus may just be beginning on the hypothesized paths of development. The most important developments occurred for independent writing, in which students exhibited increases in the frequency of phrasal features, as well as functional expansion in the use of a range of complexity features.