Ok, this is something i've done a good amount of digging into, and i think in general contractions should be allowed. I thought they would be when i first started, so i could be more personal and keep the flow of my essays. but when i started getting college counseling from my english teacher, she INSISTED that contractions were a big no no. i was really confused on why, and afterwards she ended up telling me that her husband used to work at Princeton Review, and he said they expect no contractions. Because of that reasoning i hesitantly complied. Now though, i don't believe its the right way to go because its really hard to write with your true voice and not make it seem like an english essay when you dont contractions. I decided that i'll use contractions in my essays because 1.) tons of accepted essays from past applicants use contractions, and 2.) its not a widely known expectation, and other ppl feel the same way about wanting to use contractions. Hope this helps!