Once upon a time, it was fairly common for highly educated men in the United States to marry less-educated women. But beginning in the mid-20th century, as more women started to attend college, marriages seemed to move in a more egalitarian direction, at least in one respect: A greater number of men and women started partnering up with their educational equals. That trend, however, appears to have stalled and even reversed in recent years. Gaps in educational experience among heterosexual couples are growing again. And this time? It’s women who are “marrying down.”