If you went to college and you've ever wondered why your alma mater pesters you for donations each year, it's not just about the money. Even small donations boost what's known as the "alumni participation rate." That is, the percentage of alumni who give money to the school. It's a factor in the closely-watched US News & World Report college rankings. The participation rate is viewed as an indicator of customer satisfaction. A higher rate helps attract better students and faculty, as well as other donors.

Overall, alumni participation rates have been falling in recent years. Experts say there may be some technical reasons. For example, contributions from family foundations and donor-advised funds--which are growing in popularity--don't count as alumni gifts. Colleges and universities also face more competition from other charitable causes. But there's no question that the tough economy has made it harder to raise money. Last year the national participation rate hit a record low of 10 percent.

Curious how your college or university stands up? Check out

this list

, courtesy of the Council for Aid to Education. Below are the top 20 schools:

Note: The alumni participation rate is calculated by dividing the number of alumni who made a financial contribution to the college or university during the 2009 fiscal year by the total number of alumni in the school's database. This can lead to inflated rates for schools that have small databases.

Listen to the story on alumni donations: Colleges hitting up alums early.

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