Hi Kevin! The distinction between Supporters and Defenders for Assumption questions can be a bit tricky. Importantly, it is not a distinction that will make or break you - the LSAT isn't going to dock you points because you thought the correct answer to an Assumption question was a Supporter rather than a Defender! The key to attacking Assumption questions is not identifying, "Ahh, this is a Supporter question!", but instead 1) finding the logical gap between a conclusion and its premises, and 2) framing that gap in terms of what is absolutely
necessary for the argument to function. Supporter/Defender is a conceptual tool that can help students to understand the nature of what an assumption is.
Kevin, you said that this sounded like a "supporter question". Don't think about Assumption questions as "Supporter questions" or "Defender questions". Rather, it's the assumptions (the answer choices) that fall into the Supporter category or the Defender category. For example, let's say I have this argument.
Premise 1: Texas is always hot
Premise 2: Whenever I am in a hot place, I am sad
Conclusion: Whenever I am in Austin, I am sad
There is a gap in that argument between the terms "Austin" and "Texas". (Just because most of us think of Austin as a place in Texas doesn't mean that the test-makers would agree! There's an Austin, Minnesota after all - which is certainly not always hot.)
Now that we've identified the gap, what would a good Assumption answer choice be? Well, we could have either a Supporter assumption or a Defender assumption! A Supporter assumption is one that links together the incomplete argument. So a good Supporter assumption would simply fill in the gap here by saying something like "Austin is in Texas".
Defender assumptions, on the other hand, eliminate an idea that would undermine the argument. So for my above example, "Austin is not a city located in the Arctic Circle" would function as a Defender assumption. Probably not a realistic answer choice on the LSAT, but it rules out a possibility that would certainly undermine the argument!
So an Assumption stimulus can have sometimes have a Supporter assumption as an answer choice, or a Defender assumption as an answer choice, and either one would be right! That said, certain types of gaps are more naturally filled by Supporter assumptions, while others are more naturally filled by Defender assumptions. For instance, in example about Texas that I just gave, a Supporter assumption would probably be the more likely answer choice. On the other hand, in an argument that relies upon Cause and Effect reasoning, the answer will often be a Defender assumption.
Here, for this television question, the gap is the use of Cause and Effect reasoning. Arguments that rely upon Cause and Effect reasoning are often open to ideas that would undermine the argument, specifically alternate causes. For this question, subpar schooling in the United States would be one such alternate cause of competency in math. Answer Choice (E) effectively rules out this potential alternate cause, and so it "defends" the argument. It, like many correct answers for Assumption questions that use Cause and Effect reasoning, is a Defender assumption.
Here are a couple further explanations from other Instructors on this Forum that explain the concept well:
https://forum.powerscore.com/lsat/viewtopic.php?t=12041
https://forum.powerscore.com/lsat/viewt ... =12&t=7606
Hope that helps!