From Virginia Tech College of Agriculture and Life Sciences:

What is an Impact Statement?

• Briefly summarizes, in lay terms, the difference your extension, research, or teaching efforts have made
• States accomplishments and creates strong support for programs
• Answers the questions... "So what?" and "Who cares?"
• Conveys accomplishments in simple language that is free of technical jargon

From Purdue University Agriculture:

A good impact statement illustrates change in at least one of the following areas:

• economic value or efficiency
• environmental quality
• societal/individual well being

From the February 2003 Journal of Extension:

Here is an example of a good impact statement:

"As a result of Extension-led training, 800 farmers statewide have adopted sustainable agricultural practices, including integrated pest management, crop rotation for disease control, reduced herbicide rates for crop production, refined nutrient management practices, pre-side dress nitrogen testing, and selection of crops best adapted to soils and growing conditions. These practices have resulted in reduced purchased inputs, saving more than $400,000 in pesticide costs on 28,000 acres."