Citrix vs Terminal Services

I work in a K-12 school district. We are interested in deploying a large server farm, between 40 and 50 servers, so that we can start using thin clients district wide, extend the life of some of our older equipment, and have remote information access. The question is whether to just use MS Terminal Services, or do I need to use Citrix? We have companies trying to steer us both ways. What does Citrix bring to the table that Terminal Services doesn?t? Anyone out there in a K-12 education district have any advice?