How can I find out if an accreditation is worth anything? I have found some business schools with accreditations that I have not heard of and I'd like to be sure that they are recognised.
If you cannot find sources which back up those accreditations, you should run the other way. Legitimate MBA accrediting bodies are largely limited to the big three: AACSB, AMBA and EQUIS.
Good Advice is generally correct in that if you cannot substantiate the legitimacy of an accreditation, you should be careful, especially since there are many unrecognized accreditations out there. The core accreditations are in fact the AACSB, AMBA and EQUIS, which are recognized internationally and can be read about here.
There are however, many schools who do not hold these accreditations which are still legitimate and good schools. On the other hand, when you come across a school holding a phony or sketchy accreditation, it may be worthwhile to do a bit of extra research before enrolling.