Understanding the relationship between social interaction patterns and cognitive engagement levels has critical implications on collaborative learning theory, pedagogy, and technology. This study used a multi-method approach to examine the relationship between students' social participatory roles and cognitive engagement levels within asynchronous online discussions. Results showed that students' social participatory role was a critical indicator of cognitive engagement level. Socially active students made more cognitive contributions to knowledge inquiry and knowledge construction. But there were exceptions: after taking leadership roles (i.e., discussion designers and facilitators), some students moved from peripheral participation to active participation. Second, there was a progressive development process: individual students' deep-level knowledge inquiry could trigger peer interaction, which could further advance group knowledge construction. Third, students had a tendency to keeping social-cognitive engagement patterns throughout discussions. Based on the result, this study proposed implications for collaborative learning theory, pedagogy support, and tool development.