sync multiple ipads to one computer

I agree with Thiago that this shouldn't be a legal issue. If you have 20 iPads and want to sync them all to one computer, you might want to consider looking into getting a cart or cabinet that syncs and charges all of them automatically. If you're interested there's more info available at www.ipadcart.info

There are no legal issues in syncing purchased apps to more than one iPad as long as you are the owner, which in this case is the school. All you will need to do is to verify in each iPad your iTunes account so that you can sync the apps to each iPad. It has to be same account on all the iPads.

Thiago and SKL are right - there is no legal problem in purchasing an app once and syncing it on all of your iPads.

There is one app, that should be helpful - iPhone Configuration Utility. It will help you deploy and manage your configuration across devices. Also a great resource is the iOS enterprise support page - it's full of documentation, that should be useful in your scenario.