What you didn't read was that..
That all depends on the society they live in..
Basically, if you grow up in a upper middle class town you graduate HS, no matter the COLOR of your skin.. Because chances are you parents graduated college and want you to goto college, and at a min. finish HS..
Since many hispanics and blacks in Urban cities don't have $$ or know how to get $$ for college, having a HS degree is POINTLESS.. THEY WILL NEVER GO..
Clear example the town I grew up in Flower Mound, TX had upper middle class, our school grads more than 98+% a year.. The school DIRECTLY across town, that is a lower middle area has an 84% drop out rate.
More than half of that school is eligible for free lunch..
Don't believe me, just check the Nation Statistics.. Most of the higher performing, least amount of drop out schools come from areas where home median home value is greater that 120k..