Office 365, Student Advantage Friction Free "automatic tenant join"

Starting in September 2014, students who have email addresses from schools that are eligible for Student Advantage can sign up and use Office 365 services, including Office 365 ProPlus and OneDrive for Business, simply by using their school email addresses. As soon as they sign up, students can immediately get started with the full functionality of Office.
— Office 365 Education for Students FAQ

The following may interest you if you're the AD or Identity person  for the school you work for. As of September 17th Microsoft now allows students with .edu email addresses to register for the Student Advantage program.

The Student Advantage program began in January and allows students free access to the latest version of Office, OneDrive, and some other collaboration tools. Prior to September 17th schools had to sign up for Office 365 (i.e. register for a tenant) and provision student accounts in Windows Azure AD (WAAD). That said, if you're school was eligible for Student Advantage you had to go through the motions of getting your student users provisioned in Office 365. These motions may have included DirSyncing your existing users to WAAD and depending on when you set that up you may or may not be syncing passwords so you might also be leveraging ADFS. Or perhaps you only provisioned your users in WAAD. Either way, that's a lot to manage just to get your students free Office.

So it's my understanding the point of "Student Advantage Friction Free" is to alleviate all this work and just allow students a self service method for signing up and downloading office. Sounds great right? Not exactly. If you plan to federate/sync with Office 365 in the future then your probably want to disable what they're calling "automatic tenant join"; otherwise you'll be having to clean up identities down the road prior to federating or syncing. 

How do you do this, first sign up for a trial tenant. Go through the process of verifying your .edu domain and purchase a few A2 licenses for $0.00. It's critical to purchase the zero cost A2 licenses otherwise your tenant will expire. At this point you're basically squatting on a tenant until you're ready to use it. Note, if you do plan to use the tenant in the future you should choose your tenant name carefully as it can't be changed down the line. Next, download and install the Microsoft Online Services Sign-In Assistant for IT Professionals BETA. After that download and install the Windows Azure Active Directory Module for Windows PowerShell, found here. When both are installed either import the module in your current shell or launch the dedicated Windows Azure Active Directory Module for Windows PowerShell console. Begin by connecting and logging in (you'll get a pop-up) with the Global Administrator account that was created during the tenant registration. When connected disable automatic tenant join.

Once this is done when students with .edu addresses try and register they'll receive the following message. 

The scenario below was mine which prompted me to write this post.

Scenario 3: Your school does not have an Office 365 environment connected to your email domain. If Sara signs up for Office 365 Education for Students and her institution has not yet signed up for Office 365 services, Microsoft will create an Office 365 environment with that email domain, add Sara as a user, and automatically provide the services to her account. All subsequent users with that same email domain will be added to that environment, and the appropriate services will be provided. At any time in this scenario, the school’s IT department or domain admin can sign up for Office 365 Education and start managing existing users and the service.
— Office 365 Education for Students FAQ