There are several meta analyses you can find on Google Scholar that show a weak to moderate relationship between grit and educational success. The issue appear

There are several meta analyses you can find on Google Scholar that show a weak to moderate relationship between grit and educational success. The issue appears to be that there are conflicts over what grit actually represents in this context and whether Duckworth's scale is a good measure (and if she's overselling her findings). These are very relevant questions, but they're very different from grit != success, or that grit doesn't matter.