Scroll down and select Authorise with Github
Sign in to Github
Authorise the application.
You now need to apply for the Unity / Github Student Developer Pack.
Select Get You Pack
Fill in the required details.
Select you school from the list for example select Christchurch Boys’ High School for CBHS.
You will need to upload evidence that you are enrolled at that school.
This can be a copy of your student ID.
Make sure the information is accurate before submitting as it cannot be changed.
Then you have to wait.