Sketch Cast is a site that I tried a few years ago and then was happily reminded about by Larry Ferlazzo. This is a site for creating/recording drawings w/ audio. It can best be compared to Doodle Wall or Voice Thread's doodle feature.
SC is a great application for what it does as it incorporates all of the "web 2.0" tools. However, there is no filtering going on by Sketch Cast. They have a policy in place that lets users aware of what is considered "appropriate" behavior. This lets users report abuse for inappropriate content. While this is good, it still is not ideal for schools that need to abide by strict CIPA/COPPA compliance.
Below is a quick sketch I made.
Create your sketch by clicking here.