It feels like systems like the Maturita' final multi-day exam in Italy do a pretty good job at providing students with a standardized, state-supervised process for demonstrating one's competence by the end of high school. No computers, you're under the watchful eye of your teachers the whole time, nobody knows what's going to be on the exam until the day of.
https://en.wikipedia.org/wiki/Matura#Italy
It's time consuming and nerve-wracking, but it feels fair.