If, for any reason you want to completely delete your organization, you can do so in the following way:
Click your name/gravatar, bottom of the left hand pane
Click on the name of your educational organization - under My Organizations, which is about halfway down the screen.
Click the Organization settings tab
Go to the Delete section at the bottom of the page, and type the confirmation code. Note that once your school action has been deleted, the action cannot be reverted.