How do I remove the restriction passcode on my iPad?
The restrictions password can be reset by adding a PIN to the Springboard preferences file in iOS 6.  Easier said than done!

The instructions below worked for my iPad - and no jailbreak required.   

They are, with a few minor changes, from Apple Support Community starting from about the 8th page:


Download iBackupBot
Connect iPhone/iPod/iPad via USB
Backup device to iTunes
Close iTunes (leave your device plugged in to your computer)
Open iBackupBot - this will open all device backups that it can find
Select your backup from the left column
Sort right hand pane by Path and locate "Library/Preferences/com.apple.springboard.plist" (there may be two files named this; try them both) and double-click to open
Extracted it (and only it) to the desktop.  Do this by Checkmark the file, then select the Extract Icon (or File - Export menu), then select the checkbox that says only that file and the other checkbox that says something about Info about the file.  Two files will appear on your desktop - one ending in plist and the other ending in .info. 
Edit com.apple.springboard.plist with you favourite plist editor (e.g. Xcode)
Look for and change the string for "SBParentalControlsFailedAttempts" to 0
Add in 

&lt;key&gt;SBParentalControlsPIN&lt;/key&gt;
&lt;string&gt;1234&lt;/string&gt;


after

&lt;dict&gt;
    &lt;key&gt;countryCode&lt;/key&gt;
    &lt;string&gt;us&lt;/string&gt;
&lt;/dict&gt;

Save your changes, and return to iBackupBot
Import the modified plist.  It is now in the backup!
Exit iBackupBot
Open iTunes and use Restore Backup to your device
After restore is done and phone restarts the password should be 1234.


Amazing!  But use at your own risk.

And, just to repeat, I got all this from an Apple Support Community
discussion.  Nothing is original.