In some cases your email my stop arriving in your Apple Mail app or may just simply not be working for other reasons, the simplest solution to this is to remove your email account from the iPad and add it back in again, to do this:

See below for older iPads

1. Open Settings on the iPad/iPhone
2. Scroll down to the bottom and select Apps
3. Find MAIL and select it
4. Inside here select Mail Accounts
5. Select your school account, probably called Exchange
6. Scroll to the bottom and select Delete Account
7. Don't worry this won't delete emails
8. Confirm Delete From My iPhone
9. Restart the iPad/iPhone
10. Repeat the process in reverse and select Add Account in the Mail App Settings
11. Follow the steps as normal

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OLDER iPADS

1. Open Settings (the cog) 
2. Select Accounts & Passwords on the left
3. Select your office 365 account, probably called Exchange
4. Press Delete Account at the bottom on the right
5. Press Delete to the message box (Don't worry this won't delete your emails!)
6. Let it finish and you should see that your o365 account will have been removed from the accounts list
7. Now press Add Account
8. Select Exchange
9. Enter your email address
10. Press Next
11. Press the Sign In button on the pop up dialog
12. Enter your school email address, not your apple ID (If prompted about personal or work select work)
13. Enter your password
14. You should be presented with a load of green slide bars saying Mail, Contacts, Calendars etc
15. Press Save
16. Now open the Mail App again
17. It should now be working