For our second annual National High School Essay Contest we invite students to submit essays of not more than 1,000 words on one of two topics -- "Climate and Evolution" or "Agriculture and Evolution."The deadline is February 29, 2008. Their eligibility rules are as follows:
All students in grade twelve or below in the United States or U.S. territories. Eligible students must be attending a public, private, parochial school, home school or participating in a high school correspondence program. Eligibility of prospective winners will be verified before the award of any prizes. Alliance for Science members and their families are not eligible. Essay contest judges and their families are also not eligible.
So while it's titled a high school contest, it looks like any grade-level or age may participate from 12th and below, and presumably age 18 and under.