Understanding the band descriptors is a very good way to understand what the IELTS writing test wants. and what examiners are going to check in your writing. I have taken the information below from ielts.org (band descriptors - public version) and I have broken it down for you so that you can see how the bands/criteria/scores change from 4 to 9.
Band Descriptors Task 1
Task achievement: examiners will check the overview and information that you provide; they will also check the details of your content, whether you have included all main features and the accuracy with which you have mentioned key features and illustrations. You are supposed to write 150 words for Task 1 and spend 20 mins on it.
Coherence and Cohesion: examiners will check how you organise the information, your paragraphing skills and whether you are able to use proper lexical devices (for example, linking devices/connectors (and/however/although/moreover, conjunctions).
Lexical Resource: examiners will check your range of vocabulary, whether your spelling is correct, whether you have used your idiomatic expressions, and used correct implementation of collocations and word formation.
Grammatical Structure: examiners will check sentence structures, the correct use of verb tenses, the use of simple as well as complex statements with control. At higher bands (7+) examiners expect to see more complex structures such as conditionals or passive forms.
Band Descriptors Task 2
Task Response: examiners will check if you have addressed the task correctly; they will check the details of your content, whether you are discussing/agreeing/disagreeing/listing advantages/disadvantages/problems/solutions correctly. They will also check if you have provided a satisfactory conclusion that contains a brief summary of what you said + your opinion.
You are supposed to write 250 words for Task 1 and spend 40 mins on it.
Coherence and Cohesion: examiners will check how you organise the information, your paragraphing skills and whether you are able to use proper lexical devices (for example, linking devices/connectors (and/however/although/moreover, conjunctions).
Lexical Resource: examiners will check your range of vocabulary, whether your spelling is correct, whether you have used your idiomatic expressions, and used correct implementation of collocations and word formation.
Grammatical Structure: examiners will check sentence structures, the correct use of verb tenses, the use of simple as well as complex statements with control. At higher bands (7+) examiners expect to see more complex structures such as conditionals or passive forms.
