I just found Diigo Educator Accounts, which are special premium accounts provided specifically to K-12 & higher-ed educators. Once your Diigo Educator application is approved, your account will be upgraded to have these additional features:

• You can create student accounts for an entire class with just a few clicks (and student email addresses are optional for account creation)
• Students of the same class are automatically set up as a Diigo group so they can start using all the benefits that a Diigo group provides, such as group bookmarks and annotations, and group forums.
• Privacy settings of student accounts are pre-set so that only teachers and classmates can communicate with them.
• Ads presented to student account users are limited to education-related sponsors.

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I’ve personally applied for my own educator account upgrade and I encourage anyone else with a Diigo account to do the same. In doing so, you’ll be able to continue to use your Diigo account that you’ve already setup but you’ll have additional teacher-only features that may be even more helpful to you and your students as you use Diigo in your teaching.

You can find me on Diigo at diigo.com/user/jrhode