Test like Raven's and the paper folding etc subtests of SB-LM are ungamabele...
What on earth makes you think that? I've seen an undergraduate computer science project do a pretty good job of programming how to solve Raven's, so I assume teaching children to do so would be, at the very least, no harder!
Steps onto soapbox.
People sometimes have this impression that IQ tests, or their favourite part of them, is uncoachable. I don't see how that could possibly be true. I can't think of any skill, mental or physical, that can't be improved by focused practice.
And once we're in a world where it is legitimate to have and use knowledge of what skills will be used to judge your child, i.e. some prep is allowed and there are no firm rules on how much, I think it's silly to see the parent who does most as "cheating", frankly. The rules are the rules and the parent's only duty in this context, besides following them, is to do the best for their child. The reason not to do ridiculous amounts of prep is that it might get your child into somewhere they'll have trouble keeping up. But I bet if the alternative to getting in were having the kid thrown to the wolves, no one of you would blame the parent for doing whatever prep was feasible. Sadly, to some combinations of children and schools, it feels as though the alternative isn't far off that.
I don't think you've ever had quite this in the US, but the grammar school/secondary modern divide still exists in a few parts of the UK. Children are tested (for a set of skills that are usually a good proxy for IQ) at 10 (in the 11+) and divided into schools on that basis. Parents love the grammar schools, but some of the secondary moderns, now called comprehensive but not really so, of course, are not places any of you would want to send your children. So there is an 11+ testing industry (see
http://www.elevenplusexams.co.uk/forum/11plus/index.phpfor a parent's eye view), tutoring for several years before the test is normal, and the grammar schools are stuffed full of middle class children. Does that system stink? Yes. But only the most blinkered parent of a rare HG+ child who'd ace the test without prep could blame the parents; for children with the ability the schools are actually aimed at, not preparing is foolish.
Stop thinking there's some magic way to sort children. There isn't.
Steps off soapbox
The 11+ isn't what DS is doing, incidentally.
About college essays: maybe there are places there that use them. The equivalent here is ignored for admissions decisions by the best universities, precisely because it is well known not to be an indicator of what the student can do.
