There was obviously a lot of work and thought that has gone into the grade theory, and even though it could be right, I hesitate to think it is actually grades for a couple reasons.
The main reason is because the clues we receive are for one specific person. The mole. They never refer to a group of people. Although one clue to be applied to more than one person, there has never in the course of all 5 seasons been a clue that just narrows it down to a group. Not an actual clue anyways. And this is an actual clue. Even if at the end of the season the mole happens to be someone from the "A" group, it is merely going to be coincidence just going by the grade theory and applying it to a small group. There are all types of things in the show that can be attributed to a group and at the end if the mole is in one of those groups we could say, "see, we knew the mole looked for pigs".
The second reason is based on the first reason. Not knowing how each person answered the quiz, or even if there was a tie and they had to use the slowest time, this does us no good. The clue cards and mobile text clues are based on information that they have shown us. That provides us the needed tools to apply the clue to a single person. Those two types of clues aren't based on speculation or things we have to guess about. We have the necessary information whether we realize it or not. It's just up to us to figure out the proper way to decode it.
Other clues in the show, and again I am speaking of actual clues and not just things we latch onto and think could be a clue, are provided not only for us at home but also the players in the game. Not having access to or even knowledge of the clues ABC gives us, the show has to provide additional clues so they can spot the mole. They just have to be on their toes like we do and realize they have information pointing to one specific person and figure out the way to decode it.
So I hate to say it but I truly believe we just haven't figured out the proper way to decipher this particular clue yet.
I've seen the groupings in the previous post that use the seating at the execution, and not being able to figure it out that way, I even did a new list using the seating at the meal before the execution. It gives a different set of groups but again, it is completely useless since we don't know what to do with it from there.
And in case anyone wants to try the new groupings, at the dinner table Jon was seated at the end and then 5 players down one side of the table and 6 down the other.
Craig, Bobby, Kristen, Clay, Alex....Jon on the end
Mark, Ali, Victoria, Paul, Liz, Nicole
A= Craig, Mark, Nicole
B= Bobby, Clay, Alex, Paul
C= Kristen, Ali, Victoria, Liz