EDIT2 8 September 2006: After a bit of feed-searching, I discovered that in the next few days, this essay was mentioned in hogwarts_today (link), hd_prophet (link), daily_snitch (link), and obhwf_weekly (link). Wow. Just wow.
I actually wrote about this in Dr. Nbook last year after HBP came out, but I just had a brain wave about it a few days ago. Here we go again. Duh, there are minor spoilers through HBP if you care about O.W.L. procedures, but really, who hasn't read the books by now? Of those who haven't, who would care about O.W.L. procedures?
How on earth could Bill and Percy have earned 12 O.W.L.s?
And how on earth did Hermione earn 11 O.W.L.s?
Before you tell me I'm being picky, let's look at this more carefully. Hogwarts students take Charms, Transfiguration, Herbology, Defense Against the Dark Arts (I was quite surprised to see that JKR abbreviated this in HBP, but then again, she did refer to the Marauders as such on her website.), Potions, Astronomy, and History of Magic for five years. Then there are five electives, from which most students choose two: Ancient Runes, Arithmancy, Care of Magical Creatures, Divination, and Muggle Studies. Count them. Twelve classes. This makes the possibility of earning twelve O.W.L.s perfectly reasonable.
There's a catch, though. Recall what happened in Prisoner of Azkaban when Hermione tried to take all twelve classes. She used the time turner for one year and found it too exhausting. Just one year. After this year of madness, she was down to ten classes and a more reasonable schedule.
Now this leads to a question I've been begging to ask, and should I meet JKR, I'll definitely ask her1. Hermione had to use a time turner to get to all twelve classes. How on earth did Bill and Percy do the same? Professor McGonagall had to write all sorts of letters to the Ministry and tell them that Hermione was a model student just so she could get a Time Turner; certainly the Ministry doesn't give these things out freely. This doesn't sound like something Bill and Percy would have done. There is the possibility that they didn't take all the electives for all three years, but instead took all five O.W.L.s, as Hermione apparently did.
Speaking of Hermione, let's look at her O.W.L. scores. She earned ten Outstanding O.W.L.s (in everything else) and one Exceeds Expectations in DADA. She took ten classes her fifth year, nine of which were with Harry and Ron. What was her other exam? Before jumping to conclusions, as I'm about to do, let's look at their exam schedule, which is spread over two weeks (taken from Order of the Phoenix, Chapter 31). Notes in [brackets] are my own deductions based on the other examinations.
Monday: Charms Theory (AM), Charms Practical (PM) - Harry/Ron/Hermione
Tuesday: Transfiguration Theory (AM), Transfiguration Practical (PM) - Harry/Ron/Hermione
Wednesday: Herbology [Theory (AM)], Herbology [Practical (PM)]2 - Harry/Ron/Hermione
Thursday: DADA Theory (AM), DADA Practical (PM) - Harry/Ron/Hermione
Friday: Ancient Runes - Hermione; No exams - Harry/Ron
Monday: Potions Theory (AM), Potions Practical (PM) - Harry/Ron/Hermione
Tuesday: Care of Magical Creatures3 - Harry/Ron/Hermione
Wednesday: Astronomy Theory (AM) - Harry/Ron/Hermione; Divination (afternoon) - Harry/Ron; Arithmancy (afternoon) - Hermione; Astronomy Practical (PM) - Harry/Ron/Hermione
Thursday: History of Magic4 (PM)
Now let's look at this more carefully. We see where all three of them are clearly present, for all three of them took the class and should take the exam. There are some gaps, though, where Hermione could be. My first guess was that she took the Muggle Studies exam on Thursday morning. (She couldn't have taken the Divination exam--remember, she took her Arithmancy exam at the same time) She lent Harry her notes, but otherwise Hermione doesn't appear until that afternoon during the History of Magic exam. As far as we know, there's no rule that you need to complete a course to take the exam. Hermione, being Muggle-born, is in the perfect position to take the exam. (She got a 320% on that exam during her third year, remember? Perhaps she dropped the class because it was ridiculously easy. Assuming she did take that exam, she got an Outstanding O.W.L. in the subject.) Another option is on the second Tuesday, the same day as the Care of Magical Creatures exam. We don't get much information about this day either--just about Harry's exam.
The only thing wrong with theory, though, is what Parvati Patil says after the Potions exam. She points out that there are only four exams left. Hermione protests, saying that she probably has the most difficult exam with Arithmancy. For Harry, Ron, and probably the rest of the Gryffindors, this is true. If my theory is right, though, then Hermione has five exams remaining, not four. However, it's very possible that Hermione wasn't as worried about her Muggle Studies exam as she normally is about exams.
So what did she take? When? We don't really know, but I think I've presented some options. Additionally, I think I see some house division in class selection, but that deserves an essay of its own.
1We're at the last book, so asking about stuff we're going to find out in the next couple of years isn't going to do much good. I'd rather ask about stuff we won't find out about in Book Seven.
2We know there was at least a practical examination in Herbology, as Harry got bitten by a Fanged Geranium. However, based on the pattern we see from most of the other courses the students take for all five years, there's probably a written exam as well. Come to think of it, every Herbology lesson we've seen is a practical lesson, although they do have essays and such.
3No theory exam is mentioned for Care of Magical Creatures or Divination--or for any of the electives. It's possible that these are the "applied" magical courses, for which the practical is the only exam.
4Re-enacting the giant wars as a practical examination would be kind of fun. Or rather, "What would have happened if Elfric the Eager..." Also, this is the last exam, but we all know what happens afterward.
The above text contains spoilers. It is now safe to turn off your computer.