In my continued exploration of social bookmarking, I found Forbes' October 2004 article Using Web-based bookmarks in K-8 settings: Linking the Internet to instruction, in The Reading Teacher.
Forbes describes using what I see as the progenitor of social bookmarking: web-based bookmarks. Rather than having access to other people's bookmarks and searching through them through tagging, she demonstrates the use of iKeepBookmarks as an online favourites folder. This easy to navigate service could be a better alternative to social bookmarking for teachers of young students who are using teacher-selected web pages rather than searching for their own information sources, however, older students can contribute links to the service just as they would to a class network on del.icio.us.
While tagging links and sharing them with others has great potential for young researches, the expereince is dependent upon a fairly sophisticated set of literacy skills. Web-based bookmarking is much more narrowly focused, allowing very young students or special needs students with limited reading and writing skills to experience navigating the internet. Forbes describes an activity she designed for a kindergarten class in which students navigate to two different websites to learn more about the night sky, while reinforcing an earlier lesson on recognizing the letters V and W. While del.icio.us might be a great resource for kindergarten teachers, I wouldn't dream of setting my kindergarten students loose in that text-rich environment.
I used iKeepBookmarks to create links that young students could explore as part of a prehistoric animals unit. I found the site a bit less intuitive that del.icio.us, but I still think it could be a viable alternative to social bookmarking for younger students.