Ah the beauty of technology.

Always have a document open, that way when a parent walks by we can flick to that and pretend we are editing.

If you have a Google (or other search engine) results listing up as well, you can also pretend to be researching the latest topic. Whilst you may have to do this for schoolwork anyway, you can use the online time effectively - We can hide behind research, and we can chat online to our friends - MSN, Yahoo Chat and now Twitter - multiple screens allow us to pretend we are working, but in the background our "real" work continues.