Have you tried doing some Social bookmarking or Social media optimization for your website?
Try youtube video marketing and social networking sites. They can bring you lots of related traffic.
Getting page rank doesn't mean that you will get traffic. For getting enough traffic, you have to market and promote your site properly according to your niche.I visited you site and after looking into your niche i would suggest you to promote your site through social networking site(where you will get lots of students) and through yahoo question and answer can work for you too..
That's great you have a PR6 and whatever you have done to get that, I would continue doing that.
Articlemaster is correct. The best way for your website to get traffic is promoting through social networking and Yahoo! Answers. Many students go on both and you could attract people to your site through those sites.
Continue to improve your SEO too. Never stop building links and make sure you continue this on a daily basis if possible.