Keg was correct. Rainbow's complete and utter lack of thinking in this episode was completely unreasonable. She knew she'd have to pass that test in order to get into the reserves, and yet she didn't actually think about the test at all. She didn't even start to care about it until Twilight started asking her about the test content, and Rainbow got everything wrong. You CANNOT know about a test you have to take and then not even think once about what's going to be in it - especially if you're Rainbow Dash, and you have a general abhorrence to reading.
Then, rather than sitting down and seriously attempting to study, she gave up on the first go each and every time one of her friends attempted to help her learn, saying "it's too hard" or "this is too boring". This displays a complete lack of motivation regarding the test in general, and shows that Rainbow hasn't really made the connection between studying to learn the test content, and actually applying it in order to pass. Sure, she wants to pass, but she doesn't want to put the effort in on the journey to actually passing - and Rainbow is more than smart enough to know that this is counterproductive.
Once again, she never really tries. She just says studying and paying attention is too hard, and gives up at the first hurdle......only to later get upset that she'll never pass? She has nobody to blame but herself for that, but instead she gets mad at her friends for trying to help, forcing them all to jump through hoops to solve a problem that Rainbow should have been mature enough to fix on her own. This episode made her look like a moron with the attention span of a small rodent, and then attempted to salvage that by tacking on the "I notice everything" stuff.
Why is this show so determined to make an idiot out of Rainbow Dash? She was brilliantly mature when dealing with Scootaloo in Flight to the Finish. The only thing I liked about this episode was Rarity's lines and facial expressions.
In my honest opinion, I think Rainbow Dash should have failed that test, and learned a lesson about how you won't get what you want by fucking around and not being seriously bothered to try.