When Education Secretary Betsy DeVos announced last week that the Trump administration would revisit its predecessor’s “guidance” on adjudicating accusations of campus sexual assault, she added that “the era of ‘rule by letter’ is over.” Well, not quite. A second instance of the Education Department’s overreach under President Obama, this one involving discipline in public schools, remains firmly in place.

In 2012 the Education Department released a study showing that black students were three times as likely to be suspended...