As for content, I like to emphasize understanding more than memorization. However, some test writers make the mistake (IMO) of making questions that are meant to test your understanding actually test your interpretation (the difference between the two being that your understanding reflects the concepts you've learned specific to the event, and interpretation abilities just reflects your general ability to read graphs, analyze data, etc., regardless of your preparation for the event).
I agree with most people that keeping questions of the same topic together is best for competitors, and organizing it into "case studies" is a great way to do this. Give some information (data, graphs, paragraphs, etc.) and then ask questions relating to the data. Calculations, interpretations, predictions, etc. are all good types of questions to ask. It also makes the test feel more "real" and interesting than just a stream of random, unrelated questions.
Agreed on the interpretation part; kinda like how the Science section on the ACT tests your ability to read stuff quickly rather than you know, science. Like they're important skills but they're no substitute for knowing the event. Another mistake that I've seen is when "baiting", or when a test writer is looking for a specific answer with the intention of testing "understanding" or "problem-solving", so the question is phrased in such a way to try and push the competitor towards that specific explanation. Sometimes it works, but often it results in weirdly phrased or ambiguous stuff. If the kid happens to not read it the intended way, they'll get it wrong even if they really understand the concepts behind the question. I definitely find myself guilty of doing this sometimes, but any ambiguous "leading questions" should be fixed before the final draft.
As for keeping questions of a certain topic together--it doesn't work as well for some events. For Chem Lab, it makes sense for there to be some concept mingling on FRQ questions because chemistry is often interdisciplinary. For instance, if you're analyzing its substance, both its acidity and its physical properties are of great importance. I always aim to have a cohesive "theme" or "case" for each set of questions though, because as you said, it feels a lot more "real".
Div D! I really like chem, oceanography, and nail polish--not in that order.
Troy HS, co2016.
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