This UNICEF guide provides a clear outline for writing an Executive Summary.
"Primarily for key decision-makers who do not have time to read the full evaluation report, an Executive Summary should provide an overview of the essential parts of a report: a summary of the project/programme evaluated, the purpose of the evaluation, the options used, the major findings and the recommendations. It should be very short — ideally two to three pages — and should “stand alone” (without requiring reference to the rest of the report).
The Executive Summary format below has two parts. The first part is standard bibliographical information, name of report, name of author, etc., and UNICEF-specific items, such as PIDB number, needed for report identification. The second part is the Executive Summary itself: background, purpose, methodology, findings, and recommendations. Both parts should be submitted to HQ. You may choose to use the second part as the Executive Summary inside of the report itself, but please still send both parts with the report to HQ to prevent confusion. " ("Writing a good...," 2002)