So let me get this straight: I'm about to take a major test - say, the Massachusetts Bar Exam - and you're positing to me that just before I'm about to take this test, and say I'm hanging around in the corridor outside of the room where I'll be taking the test, some person, who I assume I don't know and have never seen before in my life, says "Hey Hemingway's Ghost, I'll pay you the princely sum of $1 if you take a hit off this joint I hold in my hand BEFORE you take the test."
What's supposed to happen after that? If I say yes, do I follow this stranger into the bathroom? Do we walk out of the building and into an alley? Maybe we go outside to the street, where his El Camino is parked, and there I take the hit off the joint?
Does this strange man just hang around public buildings all day long offering people $1 to take a hit off his joint before taking tests? How many people does he make this offer to in the course of an average business day? Does he use fresh joints for everyone, or does everyone have to take one hit off the same joint? Is it good weed, or is it Mexican shake? Is it laced with anything, perhaps?
In sum, your scenario is ludicrous, and I think you, bramps, might be under the influence of some mind-altering substance for positing it in the first place. It's an exceptionally clumsy attempt at "proving your point," which is to suggest that one hit off a joint is a mind-altering experience.
Here's a shocker for you, ace: weed affects people differently. Some people could probably rip 40 bong hits and ace a differential equations exam, while others could take one hit off a one-hitter and be a little bit merry and paranoid for half an hour.
I'm beginning to think you don't know the first thing about the thing you wish to criminalize and/or turn into contraband.