Now, this seems to be one of the essays that is completely different from all the others. However, it is still one of the essays that every student in college is expected to write, especially when they are new to each class. Now, while all the other essays have their names derived from the action to be taken by the writer or what is written about, the diagnostic essay has its name from the purpose of the essay. So, when you are faced with the question, what is a diagnostic essay , just say that it is an essay that is meant for diagnosis. The major concern here is who diagnoses who. You should not mistake this for a medical a lab report format because we have mentioned diagnosis. This is simply an essay where the students’ abilities are measured by the teachers.