On the other (pre-law) board people say Adderall is great for studying and essay exams -- on multiple-choice exams it does not help because you tend to overanalyze.
There's definitely the potential of overfocusing, which isn't good for the LSAT and multiple-choice type of exams. The latter require minute analysis of the trees (OK, hyperfocus good), but also seeing the forest ... In other words, you concentrate too much on each answer (Is choice A right? Is choice B right? Is choice C right? etc.) instead of (Ok, choice B, D, E can't be right, it has to be either A or C!)
When on Adderall you tend to "think deep." But standardized tests penalize students that tend to favor deeper approaches to problem solving. Students who score highest on such tests tend to use more superficial thinking strategies than those who score in the low and moderate ranges. The lowest-ranking students employ the deep approach more often than the higher scoring ones. Standardized tests fail to measure the qualities that are truly important, reward the ability to adopt a superficial style of thinking, and in fact penalize many of the candidates with the deepest minds.
Occasionally, individual questions are defective, with the wanted answer or all of the answers being incorrect. More frequently, questions are ambiguous so that more than one answer may be defended as plausibly being "the best", and only those candidates with deep minds are likely to notice the ambiguity and be troubled by it. However, even if all the questions were impeccable, the deep student would see more in a question than his more superficial competitors would ever dream was in it, and would expend more time and mental energy than them in answering it. But the multiple-choice tests are concerned solely with the candidates choice of answer, and not with the reasons for his choise. They ignore that elusive yet crucial thing called quality.