The online collections of primary documents and digital collections are extensive and relevant to Social Studies classes in the United States.
The National Archives houses digital resources especially made for educators.
This museum in New Orleans has an enormous and multi-disciplinary bank of K-12 lesson materials. Their initiatives have included the rebuilding of naval and air force vessels from original parts with the aid of veteran assemblymen from the WWII era. Their classroom materials are put together by teachers, for teachers and include both physical and digital formats and recordings of oral histories.
This is a great resource for critical thinking about media literacy. This bank of found examples (worldwide) gives an opportunity to analyze and weigh in on the persuasiveness of various media messages that serve as propaganda. Students can participate in artifact collection and “upload” their own examples of what they consider “propaganda” on their own social media feeds!