All Useful IELTS Writing Lessons & Websites
Achieve IELTS Academic Writing Success
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https://www.ielts.org/about-the-test/test-format-in-detail This site gives you information about the Writing test from Cambridge IELTS.
https://www.ielts.org/about-the-test/sample-test-questions Here you can find sample writing tasks from Cambridge IELTS.
http://takeielts.britishcouncil.org/prepare-test/free-practice-tests British Council have free practice writing tasks on this website.