Spoken and written English

I think it all comes down to how much reading and writing students have done. Reading will help students expand their vocabulary and sample different writing styles. Even without the imitation exercises we talked about in class, reading will inevitably give students examples of sentence structure and a sense of voice. 

I'd say students who struggle to transition from oral language to academic writing either haven't had a whole lot of homework, or they didn't do it. Academic language can be "weird" and foreign. It's very formal, full of words the average student rarely uses (when was the last time anybody said "nevertheless" in a sentence), and can seem borderline archaic. I can't imagine what it would be like for ESL students because they have to write in an unfamiliar language. Foreign countries do seem to emphasis vocabulary memorization when teaching English, but it's different when you actually have to use it to convey an effective message. Picking words out of a dictionary/thesaurus doesn't guarantee proper academic language. There's an interesting line between knowing the definition of a word and the proper context in which to appropriately use it. ESL students would likely know the definition but misunderstand the context while fluent or native speakers will understand that context even if their vocabulary isn't as extensive. 

Essay writing is a skill that improves with practice, but if students have never written an academic paper before, they are not going to be familiar with thesis statements or transitions. And it's not that the material or essay prompt is particularly difficult, but I think it's that those students simply aren't used to thinking academically. Ultimately, I think the primary reason students struggle is their limited vocabulary. Yes, I know there is more to an essay than fancy words, but if a student already has a comprehensive vocabulary, then they can move onto content and organization.