I would say you have a harder chicken and egg problem than most social networking sites:<p>Normally, the value of the site to a new user increases with the number of their friends use the site, because those are the people they interact with.<p>On this site, the value to a new user is determined more by the number of higher-year students of the same school that use it, and those people are less  likely to be in that user's social network. This makes your site inherently less viral (although I hate to use the term) than, say, facebook.<p>Off the top of my head, I can't think of a solution to this problem, but maybe some relentless resourcefulness on your part can do the trick :-)