In Germany, privacy laws governing how student data is handled are very strict. German teachers are not allowed to use services where student data is stored in the US (because of the NSA and other agencies that might snoop on student data). The only way these German teachers might use a service like Quizster is by anonymizing student Ids or by using pseudonyms.
To make student info anonymous, we recommend that you instruct your students to provide pseudonyms for their first and last names in the system or just use something like "X" for their last names. Then, their only association with data will be with an email address. You could even have them set up a new email address with gmail or some other service if you want to abstract this even further.