This study examined the psychosocial skills of high school extracurricular sports activities and their generalization to student daily life. In a preliminary study, we collected a wide range of psychosocial skills related to extracurricular sports activities experienced by members of high school sports clubs, and then selected questionnaire items that would be used in the present study. In Survey 1, a confirmatory factor analysis was conducted using data collected from 376 members of high school extracurricular sports clubs (265 males, 111 females) to develop two scales, one measuring psychosocial skills in extracurricular sports activities, and the other psychosocial skills in daily life. The validity and reliability of these two 9-subscale tools, both of which comprised the same items, were thus confirmed. In Survey 2, the two scales developed in Survey 1 were used to conduct three surveys of the same subjects over an interval of about 3 months, in order to determine the causal relationships between the psychosocial skills used in extracurricular activities and those used in daily life. A cross-lagged effect model was used. The study subjects were 137 high school students who were members of extracurricular sports clubs (73 males, 64 females). The results showed that the psychosocial skills needed for extracurricular sports activities could be generalized to student daily life. Generalization in the reverse direction, i.e. from skills used in everyday life to those used in extracurricular sports activities, was also evident. Furthermore, the results suggested that psychosocial skills used in extracurricular sports activities had a cyclical causal relationship with the skills used in everyday life. Finally, the significance of extracurricular sports activities and methods for actualizing this significance was discussed based on the study results.