Crowd has contains collections of documents that the Library of Congress wants the public to help transcribe.
Anyone can participate in the LOC's Crowd project. To get started simply go to the site and click on one of the five collections of documents. The current collections are Branch Rickey: Changing the Game, Civil War Soldiers: Disabled But Not Disheartened, Clara Barton: Angel of the Battlefield, Letters to Lincoln, and Mary Church Terrell: Advocate for African Americans and Women. Once you've chosen a collection you can choose an individual document within the collection. Your chosen document will appear on the left side of the screen and a field for writing your transcription appears on the right side of the screen. After you have completed your transcription it is submitted for peer review.
Applications for Education
The LOC's Crowd project could be a good opportunity for high school students and some middle school students to learn while contributing to a national project. All of the collections in Crowd do have timelines and some other resources that help to provide context for the documents that are in need of transcription.
The Smithsonian has a similar crowdsourcing project called Smithsonian Digital Volunteers.