There are many student poetry contests, although teachers should be selective in choosing contests. Some are not choosy and publish virtually all submissions and then use this as a pitch to sell copies of the anthology. Others do create (and sell) anthologies, but are more selective. Many state poetry associations and local groups (including newspapers) sponsor poetry contests as well.

You can find listings of poetry contests at http://www.potatohill.com/contest.html and http://www.winningwriters.com/resources/ur_web_detail.php?subcategory_code=STUD.

Another option is Kids Can Publish University (http://www.fivestarpublications.com/kidscanpublish/), a web site that runs monthly contests for student work.

Good luck!