+Amy Whitfield and +Crystal Smith. They shared a number of great resources from Discus. It's always a "Why didn't I know that" kind of moment when people share the resources from Discus. There are just so many great resources available in Discus.
One resource they shared which was really interesting to me was DocsTeach from the National Archives. DocsTeach has access to thousands of primary source documents from the National Archives as well as tools and activities for teaching these documents in your class. One of my favorite parts of site is the "Activities" section. This section is loaded with interactive activities students can use to explore documents. You also have the option to create your own interactive activities with the documents.
DocsTeach site got me thinking about another great resource for primary source documents and activities. This one from the Stanford History Group Education Group. This website provides some of the same types of documents but the focus is a little different. Not only does the Stanford Group have US History Documents they also have lessons for World History. It also feels to me like the Stanford site goes a little deeper with its content.
Under the Curriculum section of the website you can access Historical Thinking Matters, a site that works to get students to think historically. The other link under Curriculum is Reading Like a Historian, this "curriculum teaches students how to investigate historical questions by employing reading strategies such as sourcing, contextualizing, corroborating, and close reading. Instead of memorizing historical facts, students evaluate the trustworthiness of multiple perspectives on historical issues. They learn to make historical claims backed by documentary evidence." If your looking to challenge your students then be sure to explore Beyond the Bubble. This part of the site allows you to assess 21st century skills with historical documents from the Library of Congress.
Take some time to explore these two sites. Both of these sites can provide you with resources to challenge your students and to encourage them to think like a historian. There is definitely a ton of information and resources available that can be used to help with close reading and other skills necessary for CCSS.