So, in the hope of helping someone else avoid the head to desk banging that I have gone through to get a Server 2012R2 KMS server to activate Windows 10 Education, I'll tell you what you have to do.

1. Install the following patch to your KMS host: https://support.microsoft.com/en-us/kb/3058168
   
2. Request the following KMS key from VLSC "Windows Srv 2012R2 DataCtr/Std KMS for Windows 10" and install on your KMS host
   
3. Slaughter a fatted calf in the centre of a pentagram during a waning moon.
   

Seems so simple now I write it down...

Oh! And note that for some reason, if you setup a new KMS host on 2012R2 the KMS listening port defaults to port 0! It should be 1688.