I'm pretty sure that MoN isn't advocating having a younger sibling inside of a backpack in the corner, btw.

DD has trouble with "pacing" and math-- she has to hit the sweet spot, or she makes a LOT of errors. The SAT was hideous that way for her. For whatever reason, that particular
type of testing environment works against her in some very specific ways, and while she eventually figured out (by experimenting on practice exams) what she could do to generally improve (she went from 93%tile on SAT to 99th on ACT), it was still frustrating to her that she KNOWS how to do things that she gets "wrong" on that kind of test.
{shrug} I don't know what to tell her (or you) about that other than to note that it's not necessarily MATH ability that is being tested for kids like this-- it's
computational accuracy under pressure, and it may not be the same thing. At all.