If so, I would suggest saying "In assessing this study, it's important to keep in mind the huge difference between grade improvement and general cognitive effects." Then, maybe you could quote a different study that found cognitive effects (which undoubtedly exist). And then, if you really thought it useful, you could say "my anecdotal experience conflicts with this" and leave it at that. But the problem with these human-interest stories is they grab people's hearts and keeping them from thinking clearly about this stuff.

Here's an exercise: try translating your anecdotal experience into boring clinical language, e.g. "one 27 year-old male subject had a small statistically insignificant increase in grades, and self-reported feeling more focused."