How do you structure an essay in History?

I would teach them my essay system which never fails. It is based on titles and sub-titles. 

I. A, B / II. A, B / III A, B

Or I. A, B, C / II. A, B, C

I often suggest the first one as many historical A levels questions are about the causes or the consequences of an event. This means with the first structure, the student can answer in a perfect three-parter: social, economic/financial, political. This allows as well for the student to save time writing the essay as they will always have this structure in mind. It is important for the first 5 minutes of each essay, to draw out this small plan.