Narrative essays are my favorite kind of essays to read, and most students find it easier and/or more enjoyable to write about themselves than other topics, but they can be problematic on a few levels. I've learned some things from my mistakes.
First, the essays can become too personal. It's amazing what students will write about. Many do not write regularly, and when they think of a personal story, they often choose the most traumatic or dramatic incident in their lives. It's important to warn students up front that they shouldn't write about anything that they wouldn't want someone else in the class to read. I used to forget to mention this at the beginning, and then when group work day came, I'd have students who would quietly come to my desk and ask not to participate because they wrote about something too personal to share. Oops. My bad. Of course I didn't make them share, but then they lost out on the benefit of the group work.
After my first quarter of teaching narrative essays, and five student meltdowns in the girls' restroom, I make sure that my students understand that although writing about a difficult subject can be cathartic, it might not be appropriate for a school essay. When I ask students to OK their subjects with me first, I invariably get a few who want to write about their brother's recent suicide or their mother's drug addiction, or some other emotional subject. Often, the act of writing brings up unexpected emotion, and I find myself in the role of grief counselor, which is not my field of expertise. Now, I counsel these students that it is extremely difficult to write about these kinds of subjects. I ask them to make sure they have enough emotional distance to focus on the craft of writing and not just the subject.
If they insist they want to stick with their subject, I counsel them to go home and write it all out in a personal journal first, to get it all out, and see what emotions it brings up, and whether they are manageable, and then focus on creating an essay. Most decide to change the subject, but some stick with it, and some have written the most incredible essays with the most difficult subjects. This is why I don't discourage it entirely. I've seen true genius.
The last problem is in grading a narrative essay. Although the elements of the craft must be graded, the students should never feel that their experience is being graded. If a student pours out his heart about his beloved grandmother and receives a D on the essay, he might feel not only discouraged about his writing ability, but he might feel as if his experience is being discounted. This is why it is of the utmost importance to remind students that writing is a skill like any other. I often use the analogy that if I was a math teacher and showed them a different equation to plug into a problem to make it easier to solve, they wouldn't be offended, and the same goes for writing - perhaps if you said it this way instead of that way, the meaning would be clearer to your readers. With narrative essays in particular, it is very important to separate the content from the presentation. I also give a lecture on how to criticize constructively and give lots of guidelines in group work to make sure any criticism focuses on the writing and not the writer, or their experience.
Narrative essays will always be a part of the composition experience, but they can also be fraught with delicate emotions that must be taken into consideration in the critiquing and grading process. I'd love to hear from other teachers on your experiences with this.