The Academic Grit Scale (AGS) is a tool to measure academic grit (passion and perseverance). “Grit” is an indicator of the level of schoolchildren’s engagement and persistence in activities. In this article, we present the results of work based on the Polish version of the AGS. We conducted the research on a nationwide group of 835 Polish students aged 16 to 19. The results confirmed the AGS’s reliability and the one-factor structure of measured academic grit. The AGS’s criterion validity was reflected in the results of correlations with locus of control, self-efficacy, and procrastination. The robustness of the results obtained with the Polish version of the AGS was confirmed through deferred measurement. The Polish version of the AGS is a valid, reliable tool that can be successfully used in research to measure grit in a group of adolescent students as it pertains to education.