There may be a big difference between the writing styles that different university departments expect (e.g. science assignments will be very different from literature assignments), so the advice below is a general summary rather than an exact list of rules.
Here are four key differences:
1. Your ideas vs research
When you write an IELTS essay, you are expected to use your own ideas because you have no access to any other sources. A university assignment, by contrast, should be based on research, which means that you will need to read books and journal articles (or perhaps carry out experiments).
2. Your opinions and the use of personal pronouns
IELTS essay questions ask for your opinions e.g. To what extent do you agree or disagree? This is more like a high school question than a university-level question. At university, you are expected to write assignments based on research rather than opinion. For this reason, it is normal for lecturers to tell their students to avoid personal pronouns (I, you, we, my). But IELTS is completely different in this respect. If you are asked to give your opinion, you can and should use phrases like “I completely agree”, “In my opinion” and “I believe that”.
3. Length of essays and individual paragraphs
This is an obvious one. You won’t be asked to write such short essays at university. The average assignment that I wrote when I was an undergraduate and postgraduate student was 3000 words long. Similarly, you won’t write two-sentence introductions or one-sentence conclusions in a university assignment; in this sense, IELTS essays follow their own rules.
4. Language focus vs subject focus
It’s important to remember that the IELTS test is a language test. Examiners notice things like collocations and two-clause sentences. University lecturers, by contrast, aren’t looking for less common vocabulary or complex structures; they want to see how well you know your subject and how well you can synthesise your research.
And which aspects of writing are the same?
Both IELTS essays and university assignments should fully respond to the given task, sentences and paragraphs should be logical, and your ideas should be developed in a coherent way. You should also avoid informal language, contractions (e.g. don’t) and abbreviations.
Can you think of any other differences and similarities?