This study investigated whether written chat-based activities foster alignment and learning of multiple simultaneously-targeted second language (L2) syntactic structures. It further examined how these were affected by prior knowledge of the targeted structures and learners' decisions to use or avoid each structure. We tested 47 Spanish first language (L1) speakers learning L2 English. In a chat-based activity with an L1 English speaker, we examined alignment in the production of three target structures that differed in their likely familiarity for participants (genitives, passives and datives) by comparing target structure production after prime versus baseline sentences. We also compared target structure production in a post-test relative to a pre-test to assess learning (increased structure usage) and we asked participants whether they made conscious decisions to use or avoid the structures. The learners experienced chat-based alignment and learning across structures. Although prior knowledge and decisions did not significantly affect alignment and learning, more prior knowledge and choosing to use the targeted structures increased overall target structure production. Thus, chat-based activities are well-suited to support L2 grammar learning, even when they embed multiple structures. However, instructors may need to encourage learners to explicitly use the targeted structures to maximize alignment tasks’ language learning outcomes.