I'm actually quite good at essays. I've been told that my writing standard is "interesting," and I know how to cite facts so that they're embedded in the writing rather than sticking out. (I keep personal goals in my essays--not repeating any word but short common words like "to be" and "the," trying to keep in at least one bit of consonance, assonance, or alliteration, that sort of thing.) I normally don't finish ahead of time (the way I do on, say, multiple choice) but I generally write a lot. Two or three pages in about fifty minutes is my normal speed.
Tests I'm generally good at if I know the material. The problem is that I have no short-term memory to speak of, so I don't cram well. If I don't know it by the day of the test, I won't know it on the test.
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cogito, ergo sum.
non cogitas, ergo non es.