A staff member has replied to your question:
SourceU accounts are no longer provided by Valve as all of the tools needed for the program are now available for free.
Each student should create a Steam account using the link below:
Create an Account https://store.steampowered.com/join
Students will also need to download Team Fortress 2 from the store page for assets:
Team Fortress 2 Team Fortress 2 on Steam
The Source SDK can be found on the Valve Developer site:
Source SDK 2013: https://developer.valvesoftware.com/...ource_SDK_2013
The SDK source code can be found on Github:
Source SDK 2013 source code: https://github.com/ValveSoftware/source-sdk-2013
If you will be using the Portal 2 Puzzle Maker students will need to purchase Portal 2 on their Steam accounts:
Portal 2 Portal 2 on Steam
NOTE: The Portal 2 Puzzle Maker is not intended as a replacement of Hammer.
If you have any further questions, please let us know - we will be happy to assist you.