I was very much the kind of student who didn't perform well under exam-taking pressure. For marked work that I did outside of school, it was straight-As for me. For written exams performed under time pressure and oral examinations (administered without advance notice), it was very much hit-and-miss.
If my son should grow up to run into the same kinds of cognitive limitations, I really don't know what I will tell him and do about it. I just wish there was a university in a Faraday cage somewhere where I could send him, so that he can have the same opportunities I had.
Fun fact on the side: Cambridge (UK) getting a railway station was a hugely controversial event at the time. The corrupting influence of London being only a short journey away was a major put-off.