This study examined the condition of Internet use and social capital, as well as its effects on teenager's academic performance. We analyzed survey data of 361 high school students. The study findings suggest that the Internet expands its reach to teenagers' school life. First, students are more reliant on the Internet to access to information that is involved in school life as well as entertainment. Second, teenagers tend to manage their social capital through the Internet. Third, the result of regression analysis indicates that Internet use time irrespective of purposes is less likely to influence academic performance, while in-degree centrality and ego-network efficiency are more likely to exert positive influence on academic perfo...