The examiners' band descriptor sheet for IELTS Writing states that a band 7 essay "presents a clear position throughout the response".
A "clear position" means that your opinion must be clear (if the question asks for it), and "throughout the response" means from the beginning to the end of your essay.
For this reason, it's a bad idea to save your opinion for the conclusion. We don't like 'surprise conclusions' in English academic writing. Instead, you should state your position in the introduction, support it in your main paragraphs, and repeat or summaries it in the conclusion. It’s very important to get the introduction right. This tells the examiner whether you are going to give one side of the argument or both sides.
For 'agree or disagree' essays, do you think you should give both sides of the argument or just one side? The answer is that you can do either.
A) Essay structure for one side of the argument:
- Introduction: topic + your opinion (either agree or disagree)
- First idea to support your opinion
- Second idea to support your opinion
- Conclusion: repeat your opinion
B) Essay structure for giving both sides:
- Introduction: topic + say that you 'partly agree'
- On the one hand,…
- On the other hand,…
- Conclusion: repeat that you accept elements of both arguments
Remember: Think of it this way: your task when you answer an “agree or disagree” question is to persuade the reader that your view is right. Each paragraph should defend your opinion.