Purpose: This paper aims to investigate the following questions--What are the types of discussion prompts in a fully online graduate course? What are the key characteristics of students' discussion initial posts and replies in a fully online graduate course? In what ways, if any, do discussion prompts influence the types of initial posts and replies in discussion threads? Design/methodology/approach: This study adopted a qualitative approach to explore the dynamics of students' knowledge construction through using asynchronous discussion boards. A total of 20 discussion prompts and 115 discussion threads from nine archival discussion boards in a fully online library science course were collected and analyzed. Findings: The findings identified open-ended, explanatory and reflective prompts in discussion boards. Students engaged in simply stating, paraphrasing, elaborating, extending, reflecting, socializing and sharing emotions in discussion posts. These findings highlighted the interconnectedness of reflection and socio-emotional interactions in a community of inquiry and pointed out their important roles to support richer and deeper online discussions. The study further observed linkages between the types of discussion prompts and the types of discussion posts. Originality/value: This study addressed an urgent need to understand the use of online discussion boards in an emergency remote teaching condition in a pandemic. The findings of this study offered educators insights into evidence-based design recommendations for prompts to support students' knowledge construction and deep learning through using discussion boards.