We designed BOOC, an application that synchronizes textbook content with MOOC (Massive Open Online Courses) videos. The application leverages a tablet display split into two views to present lecture videos and textbook content simultaneously. The display of the book serves as peripheral contextual help for video viewing activities. A five-week user study with 6 groups of MOOC students in a blended on-campus course was conducted. Our study in this paper reports how textbooks are used in authentic MOOC study groups and further explores the effects of the book-mapping feature of the BOOC player in enhancing the collaborative MOOC learning experiences.