Education subscribers will now be getting Microsoft Teams enabled by default in their tenants.
You WILL NOT be able to turn it off at Tenant level. The only way to block Teams is at the licensing level. This may pose an issue as many Education providers have several hundreds of thousands of mailboxes, and changing licensing scripts can take weeks.
The only way around this now is that you override the user subscription by turning off the service on individual services. Check your Office 365 Message Centre for more information.