The strengthen standard is the third most common task in the evaluating evidence strand, and will often be worth three raw questions on a modern LSAT. It is the logical opposite of the weekend task, but the two utilize the same thought processes until the pre-phrase.
Identifying a strengthen question is usually quite easy, as the question stems are standard and do not very significantly. A common example is: "Which one of the following, if true, most strengthens the argument?" Another common variant is: "Which one of the following, if true, lends the most support to the [speaker’s] conclusion?"
After you have identified the strengthen task, you should read the stimulus and mark the argument's evidence, bridge, and conclusion. As with the weaken task, you should be especially cognizant of the link between the argument's evidence, and the conclusion. The answer choice will acknowledge this link, and present some new piece of evidence that makes it more likely the conclusion is true.
The pre-phrase for a strengthen argument is thus, "Given the evidence that leads to this conclusion, does this answer choice make this conclusion more likely?" Again, as with the weaken standard, it is nearly impossible to pre-phrase the answer itself; the goal is to ensure that you have a clear idea of where the evidence in the answer choices should lead you.
For example: a stimulus takes evidence from a study that shows that existing entrepreneurs are much more overconfident than other business managers and concludes that must mean that entrepreneurs are more likely to be overconfident in other areas. The pre-phrase would be, "Given the study, does this new evidence mean that entrepreneurs are more likely to be overconfident?" A correct strengthening answer choice might be that those who were currently business managers but had started businesses in the past were also extremely overconfident. This new evidence acknowledges the study, and helps to show that this overconfidence is a personality trait, and not merely a result of the entrepreneurial efforts. That is, it strengthens the conclusion that people who are overconfident in one aspect of life, i.e. entrepreneurs, will be overconfident in other areas of their life and in the future, as well.
Distractors for strengthen questions will often be pieces of evidence that do not affect the conclusion directly, or only deal with the stimulus’ evidence. The new evidence could also be neutral as to the conclusion, and thus not be able to strengthen it. It is rare for a strengthen distractor to actually weaken the argument, but that sometimes can be the hardest distractor to remove as it addresses both the key pieces of evidence and the conclusion in the stimulus.
As with the weaken task, the key to successfully completing a strengthen question is to have a clear pre-phrase of the ultimate conclusion your new evidence should be leading you to.