The concept of grit has become a widely investigated topic in mental health and education in recent years. This study aims to develop a tool for measuring grit in high school and university students and to examine the measurement invariance of the developed scale on two different groups. A total of 586 high school students (411 female, 70%; 175 male, 30%) and 639 (437 female, 63%; 202 male, 37%) university students participated in the study. Grit Scale, Short Grit Scale, and Beck Hopelessness Scale were used as data collection tools in the study. The exploratory factor analysis results indicated that 14-item Grit Scale with three sub-dimensions explained 61.88% of the variance. The dimensions in the scale were named Perseverance, Commitment to Goals, and Consistency of Interest. Confirmatory factor analysis showed that the three-dimensional structure of the Grit Scale fit the data well, with measurement invariance between the high school and university student groups. Cronbach's alpha internal consistency coefficients of the total score and sub-dimensions of the scale were found as 0.87, 0.85, 0.84, and 0.75, respectively. Convergent validity was evaluated by calculating the zero-order correlation between the Grit Scale and Short Grit Scale and a significantly high positive correlation was found (r= 0.655, p< 0.001). Divergent validity was evaluated by examining the relationship between Grit Scale and the Beck Hopelessness Scale and a mild correlation was found (r= -0.484, p< 0.001). The study revealed that the Grit Scale is a valid and reliable measurement tool that can be used with adolescents and university students.