"In teaching others we teach ourselves" - Proverb
iCivics
I like iCivics because it lets students learn about civic life through experience and participation. It has games and lessons that students can work through. It also has free resources over a wide variety of social studies topics.
National Archives
https://www.archives.gov/education
The National Archives is so valuable in that it contains primary sources. Students or educators can go and read founding documents, government documents and preserved letters from their computer. It also has and educator section with lesson plans and even the ability to create your own activities for students.
Stanford History Education Group
I like that the Reading Like a Historian curriculum engages students in historical inquiry. There are lessons that focus on historical questions. It also includes a lot of primary documents which are accessible for students with diverse reading skills and abilities.
Historical Thinking Matters
http://historicalthinkingmatters.org/
This is a very cool site for teaching history. It teaches students “how to critically read primary sources and how to critique and construct historical narratives.” Rather than looking at history as a bunch of boring facts to memorize, it gets students to act as “detectives” while they use primary documents to figure out what they don’t know. It has resources both for students and teachers.
National Constitution Center
https://constitutioncenter.org/
This site is another very good site for teaching the Constitution. It was established by Congress to “disseminate information about the United States Constitution on a non-partisan basis in order to increase the awareness and understanding of the Constitution among the American people.” It has an interactive constitution where you can explore any part, amendments included. For areas that are debated, it provides scholarly articles on each side, so you can see both arguments.
Hippocampus
https://www.hippocampus.org/HippoCampus/
This site is great, first because it is free. But substantively because it has about 7000 videos, animations, and simulations on general education subjects. I like it for the content it has on history and government, but it also has math, science, and humanities. These are things that could be shown to whole classes, used for small group work, or even self-driven exploration.
Crash Course World History
https://www.youtube.com/user/crashcourse/search?query=social+studies
Crash Course is an awesome YouTube channel covering all kinds of topics. There are videos on Science, History, Economics, U.S. Government, Theater, Statistics, Media, Sociology, Psychology, Literature and more. And the videos are an interesting and fun way to supplement a lesson.
HipHughes History
https://hiphugheshistory.weebly.com/the-video-arsenal.html
This is a great source of non-biased explanations of a variety of social studies topics. HipHughes History has over 300 Instructional Videos for Social Studies teachers and students. It includes videos on US history, world history, the Constitution, government, politics, elections, and current events. The videos are quick and entertaining.