[DING-DONG YO]

[ QUOTE ]
1) Get a red pen.
2) Circle all the mistakes.
3) Draw a frowny face.
4) Hand it back to him.

[/ QUOTE ]

I do exactly this at work and I work with people that have advanced degrees. Everything save the frowny face.

Once you start making people correct their mistakes, they'll be more careful before they hand you garbage.