UPDATE: This has changed a bit now as the license centre has an online activation menu option. This will prompt you for a business Office 365 account login. Make sure your Microsoft Account you use and the Business Account on Office 365 are correct and the licenses will be added or renewed on your subscription.
If you use the Student Advantage licencing for Office in Office 365 then you will get an OSA product key. This is to activate the retail version of Office that can be downloaded from Office 365. To assign the key log in to your school’s Office 365 site and go to the link: https://portal.microsoftonline.com/Commerce/ProductKeyRedeem.aspx?paymenttype=1
This adds the license that you have purchased to be available to assign to student user accounts.
When the student logs in to Office 365 they will get an option to download and install Office.
If the school does not have great download speeds then use the Office Deployment tool to download a copy: http://www.microsoft.com/en-us/download/details.aspx?id=36778 with instructions: http://technet.microsoft.com/en-us/library/jj219424.aspx#BKMK_DownloadC2R
Create your suitable configuration file and install.
If there are errors installing it may be due to old or part installation of office on the computer. Use the tool: http://support.microsoft.com/kb/2739501 to remove any previous Office installations.