The convenience and pervasiveness of smartphones have created an environment where teacher–parent communication can be easily fostered through mobile apps. The current study aims to explore the role of instant messaging apps in teacher–parent communication. Social capital and the uses and gratifications theory were used to develop a theoretical model. The survey collected 429 valid questionnaires. The findings show that both bonding and bridging capital have a positive influence on constructs including sociability, entertainment, communicatory utility, and emotion. Entertainment, communicatory utility, and emotion have a positive influence on the willingness to use Line as a teacher–parent communication tool. The implications for the extension of communication theory and practice are discussed in the current study.