What jobs are you going to give them? Cashiers these days have Bachelors degrees in Communications. It's the inflation in the system. America is not producing as many factories as it used to, manual labor jobs in construction are hard enough to get. If you drop out, it's going to be tough to get a job.
If that were the explanation, then wouldn't we expect white drop-outs to have unemployment rates that are similar?
If you're white, you're more likely to have a father present, and not a single mother struggling with two jobs.