Well, you may already know that IELTS scores are based on a 0 to 9 point "banded" scale. But what are the specific rubrics and explanations for the writing tasks in particular?
Irrespective of whether you are taking the Academic or General Training version of the test, and irrespective of whether it is Task 1 or Task 2 on the test, your writing will always be graded according to 4 criteria:
1) Task Achievement
2) Coherence and Cohesion
3) Lexical Resource
4) Grammatical Range and Accuracy
The specific requirements for the two different tasks (1 or 2) are explained in the links provided below (direct from the official IELTS website):
Writing Task 1 (Academic and General Training):
http://www.ielts.org/pdf/UOBDs_WritingT1.pdf
Writing Task 2 (Academic and General Training):
http://www.ielts.org/pdf/UOBDs_WritingT2.pdf
So if you see that I have allocated you an IELTS score for your essay and wonder how I came to that conclusion about your writing, now you can see the actual rubrics for yourself!
Best wishes,
~ Jason