Agree with all of the above; unless the school is very reputable or an off-shoot of a well known organisation (West Midlands Police or British Airways flying club) I certainly wouldn't hand over wads of my hard-earned in advance. There are simply too many instances of clubs having folded without any warning.
Of course, with the schools that run intensive courses overseas, they will expect payment in advance, but even then I'd pay with a credit card just to get the protection that that gives.: