"America's Attic" is made up of a myriad of libraries, museums and a zoo. Think "serendipity" when using these sites - you will encounter many - many! - things that will drop you right into the most wonderful rabbit-hole of research.
This "history explorer" starts with the basics ("what is a primary source?") and takes teachers through many activity ideas and documents to use in class. Use these ideas to expand your own 'toolkit' of strategies and documents for your students. You can mix and match documents, strategies, and unit ideas with these from Smithsonian and those from other sources such as the Library of Congress, NARA, or local museum/library.