As schools deploy ipads in larger quantities it is even more important to manage the use and access of the apps that are being made available to students on the iPad. Each school needs to make their own decisions about how the control and manage iPad use by students. However, there are a few optioms school may want to consider:
The first thing you can do is set a Passcode Lock on your school iPads via Settings General, to protect your information and data.
Each time you turn on or wake up the device, you will be prompted for the passcode* before you can access applications or information on the device.
Secondly, again in Settings - General - Restrictions you can enable a range of restrictions. Again you will have to enter a 4 digit passcode*.
*Make sure you note down the passcode in case you need to change the settings at any time. If you do forget you only have a certain number of chances to input before you become locked out of your ipad and the only way to get back in is to sync to the computer you have linked as your main account.
You can see step by step instruction at 'How To Setup Parental Controls on iPad (iOS 4.2 Edition)'.
iTunes Accounts without a credit card
When you first setup an account with iTunes there seems to be no choice but to link your credit card. However, you can select to have no credit card. You can find the instructions here at the Apple Support page: Create an iTunes App Store account without a credit card.
What about if you have already set up an account and you want to remove your crdit card link. You can change your account information to remove your credit card. iTunes Store: Changing Account Information.