Not only are high-quality day cares rare, there is abundant data that day care can be harmful in large doses, especially for very young children, and particularly for boys. A Tennessee study found that kids enrolled in pre-K seemed at first to perform well on cognitive tests but fell behind their peers by third grade. “You have school systems that are pushing pre-K when they have demonstrably failing K-12 systems,” Dale Farran, one of the study’s authors told FiveThirtyEight. “It makes me cringe.”

The sort of program Senator Warren envisions has already been implemented — in the Canadian province of Quebec. Universal pre-school for just $5 (later $7) a day was introduced in 1997. The number of families placing their children in care increased by 33 percent. But a follow-up study in 2015 found that boys in day care showed more hyperactivity and aggression, while girls showed more separation anxiety. Quebec’s teenagers who had “benefitted” from the program were less happy with life in general than those from other provinces, and Quebec experienced a “sharp increase” in criminal behavior among those who had been in care.