City officials have boasted for years about their success in creating hundreds of small high schools that have higher graduation rates than many of the large schools they replaced. Now, a new report has singled out what makes the best of these small schools so exceptional.

The Research Alliance for New York City Schools picked out 25 effective small schools (whose names were kept confidential), by using attendance data, graduation rates and other indicators collected from the research firm MDRC. After extensive interviews with more than 100 teachers and principals in 2011, they found three key ingredients:

• Personalized learning environments. The schools hired key support staff, such as social workers, and created student advisory groups that typically consisted of one teacher and 10-20 students who would meet regularly.

• High academic expectations, along with support for students to succeed. The schools would offer Saturday classes and stayed on top of students with attendance issues through regular phone calls and contact with families.

• Experienced and highly effective teachers. Because of their size, the schools needed teachers who could assume a various leadership roles. They also created committees during the hiring process that included students and teachers.

Adriana Villavicencio, a research associate at the New York University-based Research Alliance, acknowledged a lot of this sounds like common sense. But she said the study got inside the “black box” of vague-sounding practices like personalized learning.

“Here we have examples of them creating specific structures like advisories with these grade-level team meetings, or small groups of ninth and 10th graders,” she explained.

One thing that apparently wasn’t a factor in success: the theme of the school. Many small schools now have themes such as law, the environment or even sports careers. While that may attract some kids, it can be a turnoff to others who wind up in the school because of the whims of the high school placement process.

Researchers also noted how little credit the schools gave to their outside partners or Department of Education networks, which exist to support them. But Villavicencio suggested the schools might not have been leaning on them as much as they did in the beginning, when they were new.

One of those outside partners is New Visions for Public Schools, which helped many small schools get off the ground. Spokesman Tim Farrell said the group wasn't surprised that the schools rated internal factors more highly than any assistance provided by intermediaries since the schools in the study were often in their sixth or seventh year of operation.

He also said called the new report validating, “since it demonstrates that the city’s most effective small schools have fully adopted the design principles New Visions has long advocated.”

The report’s authors concluded that many of these success strategies can be used in schools of any size.

Devora Kaye, a spokeswoman for Schools Chancellor Carmen Fariña, said the chancellor agreed with the report's conclusions.

"Structures that promote strong relationships with students, families and educators are essential,” said Kaye.