TRYING NOT TO LEAVE THEM BEHIND:

P.S. 397 stands at the end of a secluded stretch of Fenimore Street in Prospect-Lefferts Gardens, Brooklyn. Wayward scents, like the sizzling fish cakes and West Indian curries sold on nearby streets, do not make it here; instead, the hallways smell of Canadian bacon and cheesy beef tacos, or whatever dish happens to be on the day's menu. The school's three stories are, for the most part, subdued, except at lunch, when conversations about stuffed animals, racecars and sleepovers bring a cacophony to the cafeteria.

P.S. 397 had long tried to make a name for itself. But success in recent years has been elusive. Enrollment dwindled as families left the neighborhood or opted for charter schools with flashier offerings. Parents, many of them immigrants, were difficult to reach. More than 90 percent of students came from low-income families, and Nancy Colon, the principal, estimated that almost half of the students were being raised by single mothers.

The Common Core was the latest educational experiment to come to a school whose teachers had long tired of them. P.S. 397 embraced the standards in 2012, when Ms. Colon, hoping to shake things up, began using a curriculum from Kentucky, one of the first states to turn to the Common Core.

On its own, the Common Core was not a curriculum; it did not tell schools to use particular textbooks, lesson plans or technology. The standards provided a philosophy for instruction. Teachers would focus on fewer topics and cover each in greater depth. They would bring abstract lessons to life by explaining how skills could be applied in the modern world. And they would emphasize critical thinking at every turn.

Many teachers across the city were initially skeptical. Some saw the Common Core as another mandate from above, an idealistic vision of education promoted by outside groups seeking to radically overhaul schools.

The hurried rollout last year of a new, more difficult set of exams aligned with the Common Core to replace old exams complicated the effort. While passing rates fell across the city, the drop was especially pronounced at schools with large numbers of black or Hispanic students, according to an analysis by The New York Times. Labor unions argued that the city had not devoted enough resources to training educators in the new standards and that it was unfair to evaluate teachers using results from the new tests.

By the start of school last fall, with the memories of state tests still fresh, a sense of anxiety was growing at P.S. 397. Though teachers found much to like in the new standards and believed the Common Core could transform education in the long run, they worried about what might happen in the short term. They feared for children like Chrispin -- promising students unaccustomed to the critical thinking required by the Common Core, whose confidence was fragile and frayed.

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