Calling the bluff of a liberal community who fancies itself post-racial but is nothing of the sort.

At 7, children become very concerned with fairness and responsive to lessons about prejudice. This is why the 3rd-5th grades are good moments to teach about slavery and the Civil War, suffrage and the civil-rights movement. Kids at that age tend to be eager to wrestle with questions of inequality, and while they are just beginning to form a sense of racial identity (this happens around 7 for most children, though for some white kids it takes until middle school), it hasn’t yet acquired much tribal force. It’s the closest humans come to a racially uncomplicated self. The psychologist Stephen Quintana studies Mexican-American kids. At 6 to 9 years old, they describe their own racial realities in literal terms and without value judgments. When he asks what makes them Mexican-American, they talk about grandparents, language, food, skin color. When he asks them why they imagine a person might dislike Mexican-Americans, they are baffled. Some can’t think of a single answer. This is one reason cross-racial friendships can flourish in elementary school — childhood friendships that researchers cite as the single best defense against racist attitudes in adulthood. The paradise is short-lived, though. Early in elementary school, kids prefer to connect in twos and threes over shared interests — music, sports, Minecraft. Beginning in middle school, they define themselves through membership in groups, or cliques, learning and performing the fraught social codes that govern adult interactions around race. As early as 10, psychologists at Tufts have shown, white children are so uncomfortable discussing race that, when playing a game to identify people depicted in photos, they preferred to undermine their own performance by staying silent rather than speak racial terms aloud.