A condensed, focused summary: Give the main facts. Outline the main plot. Most importantly, make sure the specific "historical" element is clearly visible.

• Relevance: Robert Burgoyne reminds us that the most important historical films attempt to come to grips with the past, concern issues that still trouble us in the present, are about events that still have meaning for us in the present.  Communicate that relevance.
  

• Audience: Keep our general audience of high school and college teachers and students in mind, of course. But, specifically, write for people unfamiliar with the film. Perhaps especially think of helping high school and college students "shopping" for a film to view or to work on.
• Style: Communicate basic information, but write in lively fashion. Make the film sound interesting, something people will want to see, and thus your work on it will seem all that more valuable.
• Length: usually a longish paragraph -- say, 200-300 words.