How to restrict changing desktop wallpaper?

We have Macbook Airs running 10.8.1. These are exposed to students in a k-12 setting. I'd like to restrict their ability to change the wallpaper of the desktop. Is there a setting to configure?

I didn't find any way to prevent changing the desktop picture, but you could just change it back to the default every few seconds.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC -//Apple Computer//DTD PLIST
1.0//EN http://www.apple.com/DTDs/PropertyList-1.0.dtd>
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.stackexchange.apple.65938</string>
    <key>ProgramArguments</key>
    <array>
        <string>osascript</string>
        <string>-e</string>
        <string>tell application "Finder"
set f to POSIX file "/Library/Desktop Pictures/Galaxy.jpg"
if desktop picture is not file f then set desktop picture to f
end tell</string>
    </array>
    <key>StartInterval</key>
    <integer>10</integer>
</dict>
</plist>

Save the file above as /Library/LaunchAgents/com.stackexchange.apple.65938.plist, change the owner, and load the plist:

sudo chown root /Library/LaunchAgents/com.stackexchange.apple.65938.plist
sudo launchctl load /Library/LaunchAgents/com.stackexchange.apple.65938.plist

The property list is loaded automatically when users log in.