Teachers can create student logins under a teacher account. http://www.diigo.com/education . It's recommended that the teacher create a separate account from their personal diigo account, because if not then students see ALL of the teacher bookmarks.

If you're already using Delicious, you can also use Diigo without abandoning your delicous account! All you have to do is setup the Save Elsewhere function within Diigo and your links will post here and to your delicious account.

Go to your Diigo Dashboard and click My Diigo Tools.
Click the Save Elsewhere link on the left.
Check the Delicious checkbox and enter your Delicious account information.
Click Validate account.

You're all set!