Is it your belief that these people are too "dumb" to pass the test? Or are they too ignorant to pass the test?
For whatever reason, the pool of blacks who can read and do math at a 12th grade level is much smaller relative to their representation. And yet, these same guys after serving in the military and learning a work ethic (which a lot of young men acquire in the military regardless of race) seem almost universally capable of completing college level work. So, within a range perhaps, we're not talking about intelligence or common sense, we're talking about skills. Skills can be acquired.
Skills can be acquired. In theory, qualities can be learned as well but even some intelligent people seem quite resistant to intelligent organic morality, opting that they do for the canned idiocy they parrot.