Encyclopedia Britannica for educators

All California public schools now provide online access to Encyclopedia Britannica, the reputable general-knowledge source. It has all the features you would expect from an online encyclopedia --  searchable, printable, citeable -- as well as a number of additional research supports, like related articles and websites, primary sources, and leveled reading access.

Encyclopedia Britannica also supports educator uses, allowing teachers to search content by different standards, create resource packs

Here's an example of a resource pack supporting a unit on The Crucible (teachers may need to set up a free account to view materials).