Racial disparity in school discipline?

There's an article in the Oregonian today about what appears to be a substantially disproportionate percentage of black kids who are expelled and suspended from Portland Public Schools compared to white kids.

The article ponders the reason for this, and the gives us usual hand wringing about cultural bias, cultural competence training, etc.

But it never asked what I think is the most germane question: is this a question of the effect of single parent households?

I don't know the statistic in Portland, but nationally about 70% of black children are born to single mothers, compared to 30% or so for other ethnic groups. It seems entirely plausible to me that kids brought up in single parent households would be more likely to have discipline problems.

So what is the discipline rate in single parent families vs. two parent families? And among single parent families, are black kids more likely to be disciplined than white kids?

If not, then perhaps what we are seeing has nothing to do with race, but with out-of-wedlock childbirth and divorce.

Disappointing that nobody seems to be asking this question, so quick to launch down the path of institutional racism and bias.