When you receive a prompt for a diagnostic essay, consider the amount of time you've been given to write it and set aside at least 10 percent of the time for prewriting tasks. For example, if you're asked to write for 40 minutes, set aside four minutes to read the prompt and write a preliminary answer. Write a list of at least three main ideas that you will include in your thesis and body paragraphs.
Writing the Introduction
Review the three main ideas you have written during your prewriting. Begin your introduction by echoing or restating the essay prompt. For example, if you have been given a prompt asking you to write about the hardest thing you have ever done, such as moving to a new country, write an explanation of your move. Include three reasons why this task was the hardest thing you've ever done. The three reasons will form your thesis statement.
Writing Body Paragraphs
After you have written your introduction and thesis, write a transition sentence leading to your first body paragraph. For example, if you are writing about moving to a new country, write "I did not think I would be able to adjust to life in a new country." Then write about the thoughts you had before you moved. Write succeeding paragraphs about your adjustment to the new country. For example, you may devote a paragraph each to ways you adjusted to your new life. Write about how you learned a new language in one paragraph. In the next, write about how you made new friends, and specifically mention some of them.
Writing the Conclusion
Echo or restate the main points of your introduction and thesis statement in your conclusion. For example, if the three main challenges you faced moving to a new country were learning a new language, making new friends and adjusting to a different culture, write, "When I moved to the United States three years ago, I did not think I could learn a new language, make new friends, and adjust to the culture." In your concluding paragraph, mention the ways you learned the language, and perhaps some of the friends you made who helped you adjust to your new country, unifying the essay.