I'm with Turnoi on this one, but I will humour you nonetheless.

There could be a bootload of reasons why educational establishments use agents to recruit FT's.

1) They don't need to pay to advertise.
2) They don't have the time or the inclination to sift through lots of potential applicants
3) They cannot get lots of potential applicants
4) They want the contract to be between the school and the agency rather than the FT
5) They can dump the FT when he clouts a student due to the fact he didn't take his meds, then demand a replacement FT quickly.

Agents have a place. As with any industry there are good agents and awful ones. I happen to work with 2 really good ones that I have recommended to others. From my experience, agents tend to work in one of 2 ways.

1) Agents to completely avoid if you have an ounce of grey-matter between your ears. These guys will make you sign a contract with the agency. They then essentially sub-contract you out to a school. The school pays the agency, the agency pays you. My school was paying RMB14000 per teacher, for 2 teachers last semester. In both cases the FT was getting 7000. That means the agency was creaming 7000 per month (per teacher), for doing nothing.

2) Agents who simply charge a 'finders-fee' or a 'placement fee'. They do all the interviewing in order to find what their school (client) wants. The FT then signs a contract directly with the school and the school pays the agent a one-off fee.
From then on, the school deals directly with the FT and the agent walks away. This is the better type of agent (in my opinion).