This is a very useful site whenever I have to do book reports and essays since it's very tedious trying to fish through the book for little details.
The test prep section is very useful for reinforcing and helping with studying.
The articles are very informative and sometimes funny.
Just don't let your teen on this site as he/she might get carried away by the community which is really bad for children with suggestive themes. (especially in the quizzes) Some of the quizzes are down-right dirty which is NOT acceptable for any child to use. I strongly reject the idea of the site being child-safe. But it is teen-safe no doubt.
Educators should be aware that students may use this site to fudge making careful and original interpretations of literature. It can be useful -- and occasionally valuable -- to read the synopses and critiques that are offered on this site of various books. But Quasoid is correct that it is no replacement for reading the actual works themselves.