"Grit" is defined as passion and perseverance for achieving long-term goals and consists of two proposed subcomponents: consistency of interests and perseverance of effort. It has become a much-discussed construct even though research on its underlying factor structure has produced inconclusive results. Furthermore, grit as measured by its most frequently used measure, the Grit-S, does not clearly define "long term" or include the word "passion." In addition, only a few studies have looked at factor structure variation and predictive validity of grit in different age and cultural groups. We examined, using state of the art multidimensional item response models and structural equation models, the factor structure of both the Grit-S and a newly developed scale (LT-Grit scale) that specifies what is meant by long term. Participants included 1,250 U.S. high school students, 600 U.S. college students, and 500 Korean college students. We found varying factor structures for the Grit-S and a stable one-factor structure for LT-Grit, across age and culture. Perseverance of effort as measured by the Grit-S was the strongest predictor of grades in the three samples. LT-Grit predicted grades only in the U.S. high school and Korean college samples. Thus, there is no evidence that a consistent grit factor or factors exist across age and culture.