Here are sites that support teaching with primary sources, provide digital collections with primary sources open to the public that you can use in the classroom, or both.
For support in teaching with primary sources, here is ACRL's Guidelines For Primary Source Literacy-June2018.pdf (archivists.org)
Also see the Teaching with Primary Sources Online Collective
Did you know our Special Collections & Archives includes archival collections related to education and teaching?
Start California State University, Northridge, Online Archive of California (cdlib.org)
Type in "Teachers" and you will find archive collections for the California Federation of Teachers Collection, the Oakland Federation of Teachers Collection, the United Teachers Los Angeles (UTLA) Collection, the California Association for the Education of Young Children Collection, the Michael D. Eisner College of Education archives, the California School Library Association archives, and much more.