The full text of the Britannica, articles from over 70 magazines. You are able to do advanced searches. A great site for searching. KidsClick A resource based on a collection chosen by librarians. Grade range is elementary to middle school students.
Site has an advanced search section.
This site has as both free and subscription services. Search results lead to web sites, encyclopedia articles and tools. Grade range is K - 12. Menu allows you to pick grade range when searching. Kathy Schrock's Guide for Educators Highly rated site.