The purpose of this study was to investigate the mean effect size of the variables related to Grit by conducting a meta analysis. A total of 42 papers were collected for this purpose. There were four categories of related variables: school-learning factors, personal-internal factors, demographic factors, and psychological stability factors. The results of this study were as follows. The mean effect size of grit was mostly significant. The mean effect size of school adjustment was .28, and the mean effect size of academic achievement was .32, career preparation behavior was .56, and self regulated learning ability was .38. Among the personal-internal factors, the mean effect size of growth mindset was .28, fixed mindset was -.28, ego-resilience was .43, self-efficacy was .47, openness was .18, conscientiousness was .49, extroversion was .27, agreeableness was .19, and neuroticism was -.38. On the other hand, age did not have a significant mean effect size in demographic factors. Among psychological stability factors, the mean effect size of happiness was .39. Grit consists of two factors: perseverance of effort and consistency of interest. The average effect size of perseverance effort was larger than consistency of interest. The moderator analysis by school level did appear to be statistically significant on academic achievement. The average effect size of middle school students was larger than the other groups.