Preschool is a relatively recent addition to the American educational system. With a few notable exceptions, the government had a limited role in early education until the 1960s, when the federal Head Start program was founded. Before mothers entered the full-time workforce in large numbers, private preschools were likewise uncommon, and mainly served as a safe social space for children to learn to get along with others.

In the past few decades, however, we have seen a major transfer of child care and early learning from home to institution: Nearly three-quarters of American 4-year-olds are now in some kind of nonfamily care. That category spans a dizzying mix of privately and publicly funded preschool environments, including family-run day cares, private preschools in church basements, and Head Start programs in public elementary schools, to name a few. Across all of them, the distinction between early education and “official” school seems to be eroding.

When I survey parents of preschoolers, they tend to be on board with many of these changes, either because they fear that the old-fashioned pleasures of unhurried learning have no place in today’s hypercompetitive world or because they simply can’t find, or afford, a better option. The stress is palpable: Pick the “wrong” preschool or ease up on the phonics drills at home, and your child might not go to college. She might not be employable. She might not even be allowed to start first grade!

Media attention to the cognitive potential of early childhood has a way of exacerbating such worries, but the actual academic consensus on the components of high-quality early education tells another story. According to experts such as the Yale professor Edward Zigler, a leader in child-development and early-education policy for half a century, the best preschool programs share several features: They provide ample opportunities for young children to use and hear complex, interactive language; their curriculum supports a wide range of school-readiness goals that include social and emotional skills and active learning; they encourage meaningful family involvement; and they have knowledgeable and well-qualified teachers.

As an early-childhood educator, I’ve clocked many hours in many preschool classrooms, and I have found that I can pretty quickly take the temperature from the looks on kids’ faces, the ratio of table space to open areas, and the amount of conversation going on in either. In a high-quality program, adults are building relationships with the children and paying close attention to their thought processes and, by extension, their communication. They’re finding ways to make the children think out loud.

The real focus in the preschool years should be not just on vocabulary and reading, but on talking and listening. We forget how vital spontaneous, unstructured conversation is to young children’s understanding. By talking with adults, and one another, they pick up information. They learn how things work. They solve puzzles that trouble them. Sometimes, to be fair, what children take away from a conversation is wrong. They might conclude, as my young son did, that pigs produce ham, just as chickens produce eggs and cows produce milk. But these understandings are worked over, refined, and adapted—as when a brutal older sibling explains a ham sandwich’s grisly origins.