Fiona your quite mistaken about your 3 months figure. While it is true that some schools have this measure in place when working with recruiters, others do not.

I have talked with recruiters who get their payment after only a month. Others have told me they work on a half now, half later basis. It seems to be a simple matter of their negotiating skills, that's all. There is however not set, universal standard of payment, as you have layed out.