I'm sure they could have. If someone can pass that test at 8th grade, they shouldn't *have* to go to high school at all.
But there really is a difference between a GED and a tough college-prep program. That's what the "failing public schools" mantra doesn't address - that we really do have a three-tier system, one for the "remediates," a middle-of-the-road college prep, and a high-intensity college prep track taken by about 10% of the students.
That's a matter of what the *colleges* wish to do to admit someone, and I don't think that should be the engine that pulls the high school train. If an engineering school requires high school calculus for admission, and the GED barely covers geometry, it still makes no sense to expect "every child" to do the Lake Wobegon thing and take calculus. Let those who can barely master geometry take an exit exam equivalent to the GED and *leave.*