The most important thing to know about your conclusion is that it MUST ANSWER YOUR RESEARCH QUESTION. So often we see students get caught up in an aspect of their research that leads them so far away from their original research question that they have not properly answered it in their conclusion.
For more information about writing your conclusion along with excellent examples, please see page 71 of the Oxford EE Guide.
From the EE Guide:
The conclusion says what has been achieved, including notes of any limitations and any questions that have not been resolved. While students might draw conclusions throughout the essay based on their findings, it is important that there is a final, summative conclusion at the end. This conclusion(s) must relate to the research question posed.
A conclusion is not merely a summary of the main topics covered or a re-statement of your research question, but a synthesis of key points and, if applicable, where you recommend new areas for future research. For most essays, one well-developed paragraph is sufficient for a conclusion, although in some cases, a two or three paragraph conclusion may be required.
New Insight, Not New Information!
Don't surprise the reader with new information in your conclusion that was never referenced anywhere else in the paper. If you have new information to present, add it to the discussion or other appropriate section of the paper. Note that, although no actual new information is introduced, the conclusion is where you offer your most "original" contributions in the paper; it's where you describe the value of your research, demonstrate that you understand the material that you’ve presented, and locate your findings within the larger context of scholarship on the topic, including describing how your research contributes new insights or value to that scholarship.
The conclusion is a brief summary of whether or not the research question has been fully answered. It is an opportunity to give your opinion on whether or not the arguments from your research are convincing or not. It is also an opportunity to use critical thinking about your own work. Lastly, you should comment on the ways in which the Extended Essay was a learning experience for you.
Conclusion – Roughly 600 words