The National Archives has created a collection of thousands of its digital records and images to help K-12 students learn about US and world history. The collection spans the 1700s to the present, and includes hundreds of primary source documents. Students can search for records and images on a specific topic, or by historical era.
For teachers, there are resources for using the collection in the classroom. These include activities for analyzing documents, compare and contrast, finding a sequence, making connections, weighing evidence, interpreting data, and more. When teachers register for a free account, they can create their own activities on the site, and have students login to participate in them.
There is now an app version of National Archives DocsTeach available for iPad only