There are many excellent Science Apps for iPads. Following is a list of Apps that I have used and recommend. Some of these are free, some are paid but are an excellent value. If you are using Apple Configurator or any device enrollment software at your school, you may be able to push these out to all devices enrolled. Most of these are rated for Age 4+, but some are 12+. Please confirm age appropriateness for your grades. Confirm iOS version requirements. There may also be versions for other platforms and operating systems.
Science Apps for iPad