Cheers, drynxz (excuse the pun - or am I attempting to pronounce it incorrectly lol)
UMAT prep programs really are a bit dodgy. In retrospect I have to doubt whether it actually helped me at all. I think UMAT is something that you just either have a knack for or you don't (esp sections 2 and 3)
One thing to be wary of is the claim of some people ( *cough* medentry *cough*) that in the actual exam you will achieve percentiles of at least around 15 higher than in your practice exams. From the beginning I was consistently achieving about 90-95th percentile (s1), 85th percentile (s2) and 95-100th percentile (s3). In the end I got (98th/74th/100th) - yeah wth @ section 2?!?!
What I'm trying to say is that if you achieve say 70th percentile consistently in practice exams, don't think "sweet, I'm a shoe-in to get 85th percentile cos in the practice exams I'm competing against a "more able and dedicated cohort"" because overconfidence is a killer and people are too quick to believe these sorts of programs.
In terms of how they "scale" UMAT marks - they scale them so they are relevant over a 2 year period. That means if one year's test is ridiculously hard and the next year's one is ridiculously easy, for a similar overall percentile comparing to your group (i.e. 2 people both get an overall percentile of, say, 80), a person who did the harder test will get a higher mark than one who did the easier test (they do this to account for small variations in test difficulty from year to year)
If you really want some indepth discussion from people who actually know what they're talking about, join something like MSO or read through the forums.