For reference, I've taken: Biology, Calc AB, Calc BC (self), Chem, Micro (self), Eng Lit, Env Sci (self), Euro His (self), US Gov (self), Psychology (self), Stats (self), US His, World His (self), and Chinese (native). I received 11 fives, 2 fours, and 1 three.
All of the following commentaries are based on my own experience. In the cases where I have not taken the course, the general sentiments conveyed by the test takers I know are presented.
Do I Need a Course?
There are some AP exams where it might be more difficult to self-study if one doesn't have extensive prior knowledge. In these cases, it is much easier (and to your advantage) if you just take the course. Fortunately, most of these courses are offered even in schools with a small AP curriculum.
IMO, I think these courses are better (and significantly easier) with a teacher:
Calculus (without prior calc knowledge), Chemistry (for the labs), English, Languages (non-native ones), Music, Physics (depends), Art (practical), US History (for DBQs).
I think there are four subjects that lay the foundation to a good AP test taker's arsenal of AP knowledge: Calculus, English, US History, one non-Bio science AP. These exams should not be taken as self-study as Calculus teaches important mathematic concepts for university math that one might not be able to glean through self-study, English teaches essay writing skills (a prolific AP essay writer can raise his/her scores across the board by 1 point), US History teaches DBQ skills (good for History APs), and Chem/Physics teaches lab (chem) and scientific theory (physics). I would take Chem in school because of the labs (labs cannot be replicated through Cliff Notes write ups) and I would suggest only self-studying Physics (C) if one has a solid science base and is relatively adept at Calculus.
Self-Studying History APs
I took all three history APs and received 5s on all three. I would say that Euro and World History are some of the most interesting APs one can come across. The best thing is, they can generally be taken prior to APUSH (meaning, you could start on them in frosh/soph years). Euro and World both have a simplified form of the APUSH DBQ, so essay writing is not going to be a big deal in these APs. History APs are reading and writing intensive, so self-studying these courses are good humanities supplements to a strong AP science base. If you can take the whole set and get reasonable scores, I think this boosts the app in terms of academic ability and highly supplements the application.
"Easy" Self Study Exams
Now, there have been numerous threads on this topic. There are some extremely easy AP exams to self-study. I give them below and follow them with some pointers:
Environmental Science - This is a relatively straightforward exam that attaches nicely as an extension to the Ecology portion of Biology. Highly managable in a short time, Environmental Science is a combination of common sense that you already know (gleaned from mass media and general books) and just a few more ecology concepts. This is a good AP to self study right after taking or studying Biology.
Human Geography - Not having taken the exam, I can't comment extensively on this, but I've heard that this is THE easiest AP exam and there isn't too many advanced concepts covered. Perhaps would work good as a humanities supplement?
Psychology - Again, this is a popular self-study topic. The study of Psychology is extremely broad, but AP Psychology tests an extremely small subset of Psychology (that is already extensively covered in prep books). This is a self-study AP that you can take just through reading a prep book.
Art History? - Many people take this to fulfill the a-g Fine Arts requirement for UCs. I'm not particularly sure how simple this exam is, but many people claim it is highly managable through a textbook and serves the a-g requirement nicely.
General Self-Study Courses
Biology - Bio, IMO, should be the only AP science that should be self-studied. Biology is highly straightforward, as most of it require the memorization and assimilation of concepts. In fact, many people report scoring 5s on Biology just through reading through a prep book. Although I do not advise this route, Bio is the most easily managable science AP and should be considered, if taking AP Bio is not an option at school.
Economics - This is an "easy self-study" AP, but I would say requires time and is definitely not as easy assimilated as Env Sci and Psych. The AP exams also tests a very small subset of the entire study of Economics, but the various graphs and figures in Economics pose a greater obstacle than just a "breezy" self-study AP. Should be attempted with plenty of time (not a few days before the exam).
Government - Government is easy to self-study, sure - but it's very hard to get a 5 without good knowledge of the subject matter. Only 8.0% got a 5 in US Government in 2006, so it's not a self-study course that is just a "blowoff." Having a strong APUSH background will help for US Gov - aim for the details. One can probably get a 4 through attacking the gist of things, but to get a 5, you have to have detail. Advice: don't rely on prep book material alone.
Physics - Assess your scientific performance and decide whether to approach. Physics B is highly managable with just one year of general Physics, but Physics C might require more thought and specialized knowledge, especially Calculus. Physics C is actually one exam I regret not having self-studied in high school. The scientific knowledge contained within it is quite essential for future courses.
Statistics - Easy to self-study, but make sure you know the concept of "null-hypothesis testing" before venturing into the exam if you want the 5.
General Self-Studying Advice/FAQ
For subject matter containing a lot of material, start early. You cannot viably cram 6,000 years of world history knowledge in 2 nights; neither can you learn the different market systems in Economics in 1 night (I found out the hard way).
It is possible to fit self-study APs along with your school schedule. Set aside about an hour each night starting from January/February and work your way continually through May. With perserverance, it's not hard to get a 5 in many self-study exams.
Remember to register with your school in January/February about the exams you're taking in May. If you don't check in with them, they'll just register you for the AP exams you are taking at school.
Don't overload in certain topics (for example: don't take all 3 history APs and English in one year) in a certain year. Plan accordingly and well so that you can maximize your score, not just the number of AP exams you are taking.
Self-studying three exams and getting three 5s is more preferable to self-studying six and getting 2, 3, 3, 4, 5, 5. If you are not ready, don't take it.
You should be able to walk into testing confident that you will have a decent score (i.e. 5, maybe a 4). If you are self-studying APs, I assume you are aiming for HYPMSC schools - they are generally indifferent towards 3s and 4s.
If you want, aim to be National Scholar at the end of junior year. Take eight AP exams and score higher or equal to 4 on all of them.
Don't overload yourself on too many "small" exams (Env Sci, Hum Geo, Psych) and sacrifice your score on the "big" (and more important) exams (Physics, Calc, English).
If you are contemplating on self-studying APs, you probably have the intellect necessary to do wonderfully. Self-studying APs is a question of discipline, not of sheer brainpower.
AP exam scores are not the most important components of your application, but they can really bring out your initiative when you perhaps cannot demonstrate your academic prowess otherwise. For example, how can you convey the fact that you do have the ability to do 8 APs in one year if your score does not even allow you to take more than 2 in a year? How can you demonstrate that you can take more than 15 APs when your school only has 5 (maybe less) AP courses? I'm writing this generally toward the smaller-school audience, not the prep school or magnet school types.
Questions, comments about self-studying? I'd be happy to answer them :]
