I don't know about the A-Level Maths. I presume it's more like the Irish exam, but maybe more advanced because Irish students study more subjects in secondary school than do students in the UK (?).
A level is also very routine (not as routine as SAT, but it has a different role: not every successful 18yo taking A levels takes A level maths). The alternative qualification Pre-U was designed to be less so.
On the other hand, the SET program at Hopkins is focused specifically on getting a score of 700 before age 13. To get there, a kid would have to have finished geometry and have got partway through Algebra 2. This is because the SAT does test facts that can't generally be intuited in the 45 seconds or less that you get for each problem.
If you have time, could you look at the currently available full SAT practice test at
http://sat.collegeboard.org/practice/sat-practice-testand tell me specifically which questions you think require the student to have finished geometry and got part way through alg 2? I'm really not seeing it. I see a couple of uses of "vertical angles are equal" for example, but if the ALEKS syllabuses are a reasonable guide, that's in 6th grade maths. And I see some places where you have not to be scared by exponents, or by the idea of a variable being used to mean a number (both well covered in prealgebra). Beyond that?
ETA: Remember also that the SAT is grueling (ten subtests and 5.5+ hours from start to finish). So getting through it at a young age also requires an ability to concentrate for a long period that most kids that age don't have yet.
I'm not disputing that young children who do that well are unusual. Indeed, they probably do tend to be exceptionally mathematically talented by correlation, or by accident if you like - parents who think to put their children in with this in mind probably do so because they think their children have exceptional mathematical talent - but I don't see why I should believe that the test itself would be a good filter for that.
Personally, I think a homemade exam would be better, but then Hopkins would have to write one or two exams per year.
Not necessarily. They could, if they chose, use exceptional success at an exceptionally young age in the AMC tests, which are getting set anyway, for example. My guess, though, is that this system seemed like a good idea once upon a time, and nobody has had a reason to change it. Sounds more as though SET hasn't been killed yet than as though it's really alive.
