It seems you have done enough link building and you already have a good amount of traffic and rankings. [IMO] try to gain returning visitors. Have you analyzed your stats from where you are getting most of your traffic e.g direct, link referrals or SE's.
Since your site is education related, social networking and word of mouth publicity will be the best campaign (IMO) try offering some freebies to visitors and become more active in Social networks.
Also i found the
good thread here discussing similar questions, you may find answers here.