Creating Usernames and passwords for a class

I am keen to hear what strategies  teachers have been using to setup and track new classes on Scratch 2.0?

We've been introducing Scratch to 4th graders for 4-5 years now.  Students save their work to network shares, on which teachers have read-write privileges.  That makes it easy for me to track and evaluate student work.

For 2013-2014 I'd like to start using Scratch 2.0.  I am NOT keen to have 4th graders choosing new usernames and passwords for every web-based app they go to.    And even if I could swing that, I am not sure how to track student work.  

All our students have Google Apps accounts, so using Google Authentication would certainly be a plus for us.

Thanks

Santosh