This classroom study aims to explore the instructional effects of structure-based (SB) or dynamic usage-based (DUB) instruction with free response, communicative writing tasks after three years of L2-French instruction on linguistic complexity measures in (morpho)syntax and lexicon. We investigated data from forty-three young high school beginner learners of L2-French after three years of instruction with similar amounts of L2 exposure. The SB treatment included a traditional focus on explicit grammar; the DUB group was taught using the Accelerated Integrated Method, a highly communicative, meaningfocused method without explicit instruction, but with a great deal of exposure and repetition to induce frequency effects. Results after three years show that DUB instruction leads to more linguistic complexity in terms of various (morpho)syntactic and some lexical measures (multi-word sequences coverage). On other lexical measures (such as Guiraud index and average word length), no differences were found. The results are discussed using insights from the dynamic usage-based perspective.