The use of text chat in synchronous computer-mediated communication (SCMC) could help remedy the widely reported lack of active involvement in online language learning. However, the nuances and complexities of learners' text-chat actions warrant further examination. This exploratory study used observational data collected from 40 students in a graduate-level Academic English course at eight time points across a semester to analyze the functions of text-chat interaction in an SCMC setting and to capture how their text chat changed over time. This led to the identification of five functions of text-chat interaction (i.e. cognition, metacognition, socio-affect, organization, and technology), suggesting that cognitively meaningful learning occurred immediately through such interaction. Over time, there was a decline in the quantity of text-chat interactions. In addition, the patterns of chat between students and the teacher were somewhat different from those observed among students. In the former case, text quantity diminished, especially in the category of cognition; but in the latter, students engaged in more text chat with their peers to show affect, cognitive agreement, and disagreement over time. The study's findings regarding the complex dynamics of an authentic process in SCMC language classrooms have considerable practical value in facilitating interaction in similar language-learning contexts.