This cognitive lab study examined how secondary students in Grades 7-12 interacted with an AI-enabled chatbot while completing online course activities. Using chat logs, facilitator observations, post-session reflections, and survey responses, we analyzed spontaneous and lightly seeded interactions to evaluate whether the chatbot supported its intended theory of action: helping students continue learning without simply completing work for them. Findings highlight the importance of typing fluency, answer-boundary handling, safety and privacy response patterns, and student-facing feedback mechanisms. This study illustrates how cognitive lab evidence can inform ongoing validation.