In an effort to investigate developmental episodes in additional language learning using both cognitive and social frameworks, this working paper presents results of a pilot study based on a task-based language learning session. A total of forty participants at a Japanese university carried out a pedagogical task in five steps, including both interactive and independent steps. No instruction was provided. Approximately 3,000 responses were collected and examined for comprehension of target forms, and for the rationales provided for form selection. The quantitative analysis indicates significant gains in comprehension and the qualitative data show a shift in the trajectory of participant thinking as a result of participating in a task session. Commentaries from participants provide insights into the social and cognitive aspects of their developmental processes.