Perhaps districts create CDO positions because they have larger achievement gaps that they wish to remedy.

That was my first question. Well my second. (See below the line)

To address this concern, it is possible to examine the trend in achievement gaps, over time, rather than the static magnitude of those gaps, to see if districts with CDOs are making progress to close those gaps.

Unfortunately that too is not independent. Racial Socioeconomic Inequality Predicts Growing Racial Academic Inequality.

To see if a CDO improves the performance of the blacks and latinos you have to make a fair effort to estimate how they would have done without the CDO. Assuming that they would have done the same as schools without a CDO is accepted by the paper to be questionable. Assuming instead that the relative trend in performance would be the same, as they have done, is also questionable.

But come on:

1) Chief diversity officers (CDOs), who typically advance a leftist agenda, are spreading beyond college campuses and becoming more common in K–12 districts.

Really? You're going to make it clear that you've got a political bias, at the front of your paper?

Why?

A reason that will be well known to a think tank is that if you associate an argument with a political position, people that feel part of that political position are loathe to question the argument, and quick to dismiss counter-arguments without considering the content.

A paper that leads with "these results are for conservatives only" by a think-tank should ring alarm bells. If they genuinely believe that they have a sound argument, they could present the evidence so that it can sway everyone. If they feel the need to leverage people's politics, and thereby limiting the target to only conservatives, it's likely that they know that their argument doesn't stand analysis.