This study investigated how the different discussion approaches in Facebook influenced students' scientific knowledge acquisition and the nature of science (NOS) views. Two eighth- and two ninth-grade classes in a Taiwanese junior high school participated in the study. In two of the classes students engaged in synchronous discussion, and in the other two classes they engaged in asynchronous discussion. The 83 participating students discussed scientific news that had been posted on Facebook, with a total of seven news stories. Three instruments--a general NOS views questionnaire, a content-related NOS views questionnaire, and a science knowledge test--were administered before, immediately after, and three weeks after the intervention. In addition, student responses to each news story were collected and analyzed. The results demonstrated that regardless of which online discussion group they participated in, students improved their science content knowledge, general NOS views, and NOS analyses of scientific news. Especially, synchronous discussion proved more effective than asynchronous discussion at helping students to develop science content knowledge and increase their view of community aspects of content-related NOS. These findings demonstrated the advantages of quick feedback and responses in synchronous discussion facilitated communication and cognitive development about subject and subject-related nature of science.