In an increasingly digital society, educators are encouraged to use synchronous online technologies. This study attempts to explore the community of inquiry in a web conferencing system through synchronous interactions and focuses on the relationships between cognitive presence and academic achievements. Participants were teacher candidates enrolled in a one-semester synchronous course at an online program of a public university. Community of Inquiry Questionnaire, final exam scores and student discussion messages were used to gather data. Results indicated that while moderate positive relationships were found between cognitive and social presences, no significant correlation was addressed between teaching and social presences and also between teaching and cognitive presences. In addition, cognitive presence was found moderately positive correlated with academic achievements. The role of the instructor and the affordances of web conferencing system positively influenced the students' cognitive presences. Further research directions and practical implications about the synchronous instructions were also included.