Speaking of graffiti, here's another online opportunity for you and the kids. Draw Ball is an online collaborative art project; its basically like a big graffiti wall that you can only work on for a short amount of time per day in a limited amount of space.

One of the interesting things about drawball is that the limitations have given rise to some creative solutions - various online communities have organized communal paintings. With multiple people working in various 'sectors', some drawings will stand out due their size.

Until, that is, the tide of graffiti swallows them up again.

As with Pictaps, this site is open to anyone with internet and an active imagination. It may (or may not) be something you want to use in your class, but at the very least, it gives us another imaginative way to create art with web 2.0.