The indefatigable Debbie Stier asked me for my take on this the other day, and I realized that I had never written about it on this site. My answer to all of the above is a qualified "no." There's a bit of truth to each claim, and you won't have to look too hard to find people who'll argue for any of them. You might even have a friend with a crazy theory of his own (Duuude, the SAT is an awesome predictor of alien abduction!). I've been working with the SAT for a while now, and I've come to my own conclusions.
The short answer: there is no short answer. Each subject tests different things, and although there are overarching themes, you're not giving the test fair treatment if you try to encompass the whole thing in just a word or two. What follows is a bit of a brain dump. Chime in in the comments if you think I'm missing something.
- Deep Reading: Are you able to interact with a passage in such a way that you understand the author's tone? Can you draw inferences about how the author might respond to counterarguments or criticism of her point of view? Do you understand why she might have bothered to sit down and write the passage in the first place?
- Precision: Do you comprehend sophisticated writing (both in the passage and in the answer choices!) well enough to pick the one correct response from a list when the incorrect choices are often incorrect for subtle reasons? Often incorrect choices can be eliminated because of a single word in the choice! Do you know exactly what words mean? On hard sentence completions, it's not good enough to have a vague sense that a particular word is "positive" or "negative." You have to know precise definitions, and recognize appropriate use (not for every single word, mind you, but for enough to successfully eliminate incorrect choices).
- Vocabulary: This is a corollary to the above, but obviously you need to possess a decent vocabulary to score well on the CR section.
- Umm...math: How are your fundamental math skills? Are you comfortable working with right triangles, exponents, and percents? Can you reliably translate word problems into mathematical equations? There's no way around this; there are many techniques that can help boost your score, but if your fundies are weak your score will be also.
- Nimbleness: Do you see multiple ways to solve many of the problems? Are you willing to take shortcuts if they're available (like on questions like these), or are you dogmatic in your methodology? Are you able to transition easily between techniques if the first one you try doesn't bear fruit? Are you willing to try crazy things if you're stumped?
- Stick-to-itiveness: Do you persevere when your first approach comes up empty? I've been teaching this stuff for years and I don't get questions wrong when I take the test, but that doesn't mean I still don't end up at a dead-end once in a while on my first go-through of a problem. The highest scorers cock their eyebrows, learn from their missteps, and reroute when they run into trouble.
- Grammar: Can you spot common usage errors? The SAT doesn't cover every grammatical rule, and it stays pretty far away from most grammar controversy. (Oxford comma? Not tested.) If you know the most common SAT rules, you'll be in pretty good shape. If you're looking for an exhaustive list of rules, Erica Meltzer's got you covered.
- Flow: Can you identify (in the multiple choice) and execute (in the essay) a logically structured, well formed sentence or paragraph? Are you able to recognize when contrast or transition words are appropriate, or when an edit might drastically improve clarity and readability?
The Bottom Line
It's quite difficult to say, concisely, what the SAT is testing, and attempts to do so are often uselessly reductive (it's what you learn in school!) or dismissively curmudgeonly (the SAT tests you on how well you take the SAT). Students who work assiduously in school (not students whose grades are exemplary because of cramming skills) tend to do well because there is a fair amount of overlap between SAT skills and the skills ostensibly taught in high school, but it's also very possible to raise SAT scores a great deal with focused prep because the SAT is fairly predictable, despite its breadth.
Regardless of what the SAT tests, your score is not a number that defines your worth. It is not tattooed on your forehead, and once your senior year is over it will very quickly be relegated to a dusty, rarely-traveled corner of your mind. As crazy as this may seem to you now, you might get to a time in your life when you can't even remember what your SAT score was. But it is a number that may help you gain admission to the schools you pine after, so if that's important to you, then you should take the steps to ensure that you'll be happy with your score.