This is a Weaken question. Essentially we want to weaken the conclusion and/or the relationship between the conclusion and the premises. The first thing to do here is to find the conclusion (the second sentence).
The support for the conclusion is largely the last sentence, that most of the children who saw the film punched Bobo the Clown, while most of those who had not seen the film did not. However our conclusion is about children hurting other children, not Bobo the Clown. (Notice that even though the conclusion does not directly reference children hurting other children, it does reference “this aggressive behavior.” That line refers to the first sentence and therefore the first sentence is, in essence, also part of the conclusion). We want something that distinguishes between Bobo the Clown and children.
A. Some of the children? Way too weak. "Some" just means 1 or more. That is not a strong enough statement to weaken the conclusion here.
B. This is similar to answer choice A in that it is too weak. Merely because one student acted in a particular manner not does detract from the evidence that most students who saw the films punched Bobo, while most students who did not see the films did not punch Bobo.
C. This directly weakens the argument. Notice that this weakens it by dismissing an unstated assumption in the argument (that Bobo the Clown is an accurate stand-in for children in general). Some people would dismiss this answer choice because they think it contradicts the premises, but it does not. What it does do is make the premises useless and unsupportive to the conclusion, but it doesn't contradict them. This is the correct answer.
D. This could only strengthen the argument because it provides evidence that the film did cause violence... even kids who didn't see the film, but knew other kids who saw the film, ended up punching Bobo. So it's a strengthener, and it's a weak strengthener at that because of the "some."
E. Having seen a Bobo Doll before or not is irrelevant and doesn't weaken the conclusion at all.
About Larkin: Larkin Robson is an LSAT Tutor and Attorney based out of New York City. He has a JD from NYU School of Law, has taught at West Virginia University School of Law and John Jay College in Manhattan. He has been teaching the LSAT for 8 years and founded an independent boutique LSAT company called 180 Degrees LSAT. Like Nathan, he scored a 179 on the actual test. His website is 180degreeslsat.com Tweet him @180degreeslsat.
From Larkin: I like the LSAT because there is actually a reason for the test. It is testing critical thinking and reading comprehension, both skills that are useful and valuable in the real world. I am a die hard philosophy buff and I think that the humanities and critical thinking are vastly undervalued in today's society, and the LSAT is essentially testing those skills. It means that studying for the test does not mean you are just studying for a stupid test, you are actually learning something useful.
Please ask questions and/or suggest corrections to anything that seems confusing... we want to make this the best resource we can for LSAT students. We'll have all the June 2013 explanations up as quickly as possible. Thanks for reading. Tell your friends! --nathan