Cannot erase iPad without iCloud password
I have an iPad used in a school setting. A student no longer at this school signed in with her icloud account. After upgrading to IOS7 I am unable to erase this iPad and remove this icloud account. I have tried but keep getting message to turn off find my Ipad and cannot do this without password. I cannot delete and erase all settings without password. I cannot sign out of icloud account without password. Please help me get out of this loop.
iPad 2