The iPad has great battery life. The battery can be expected to last for up to 10 hours under normal usage.
Charge your iPad every night!
Obviously the simplest and best way of making sure your iPad has enough staying power for the school day is to charge it every night.
If, in general, your battery life is consistently short and you're basically just watching the indicator drain down before your eyes, here are some things to try.
1. Restart your iPad
If you haven't rebooted in a while, give it a try. There could be a rogue process or something else doing what it shouldn't be doing, and a hard restart can often fix that. This can be performed by clicking and holding both the power button and the home button at the same time for 10 seconds.
2. Power Cycle
About once a month, and certainly if you're having problems, you should completely drain your iPad's battery (drain it until it shuts down on its own) and then charge it back up to full.
3. Turn Off What You Aren't Using
Anything running on your iPad uses up the battery. So if you've tried everything else and it turns out you're just using your device more than the battery will allow for the length of time you need to use it, you'll need to make some hard choices. You'll need to stop using some of the features you don't really need in order to keep using the ones you do. The more you turn off, the longer your batter will last but of course the less you'll be able to do. It's a balancing act but one that can help you squeeze out a little extra juice when you really need it.
Turn off Location Services. Go to Settings > Privacy > Location Services, and turn off any app you really don't need tracking or using your location.
Turn off Push Notifications. Likewise, go to Settings > Notifications and turn off any app you don't care to be alerted about.
Turn of Notification Center widgets.
4. Miscellaneous Tips
Turn off "Background App Refresh" in the "General Settings" of the "Settings" app.
Turn off any extra sounds, like keyboard clicks
Turn off the iPad sound EQ
Use headphones instead of the speaker if you have to listen to audio or music.
Turn down the screen brightness