Websites

When it comes to the English language, grammatical mistakes seem to be a common occurrence. While I can tell my 13 year old son that the sentence construction is not correct sometimes its a bit difficult to actually tell him why.

Can anyone suggest some websites that deal with elementary grammar?

Any help will be much appreciated.

This looks pretty good. I don't know if it's elementary.

[Dead link removed - ed]

Then there's the Schoolhouse Rock videos. And my son liked a book called "The Transitive Vampire: A Handbook of Grammar for the Innocent, the Easter and the Doomed" by Karen Elizabeth Gordon.