This study examines student engagement patterns in Small Private Online Courses (SPOCs) by analyzing 752 discussion posts from undergraduates. It explores the relationship between engagement behaviors and course performance, using a behavioral coding rule and an emotion lexicon to assess posting behaviors and emotional trends. Key findings include: high-performing students were generally more active in engagement behaviors (excluding interactive postings), registered students contributed more threads and used richer vocabulary, emotional expressions did not significantly vary by registration type but showed increased confusion among registered students towards the end of the semester, and positive emotion was prevalent across the board, with high-performing students exhibiting greater emotional density in all three types of emotions (positivity, negativity, confusion).