What makes a good charter school? The same things that make a good school run by the city, Chancellor Carmen Fariña said during her first two school visits of the year.

The Monday visits were to two charter schools, Girls Preparatory Charter School in the Bronx and Growing Up Green Charter School in Queens. There, Fariña played down the political tensions that have flared up between the de Blasio administration and repeated her ideas about what makes a high-quality school: having an effective principal, retaining teachers, and making good use of time.

“That, to me, is key for any school that’s going to be successful,” Fariña said, noting that she was particularly impressed that 15 of the 23 teachers who started in Girls Prep’s first year in 2009 remain at the school. “The retention rate of teachers is a high mark no matter what school you’re in.”

Fariña has made it clear that she is focused on students in schools that she runs, and her tours — alongside New York City Charter Center CEO James Merriman — were a notable foray into charter schools, which receive public funds but aren’t required to abide by many city and state regulations. Fariña has visited a number of other charter schools in her year and a half as schools chancellor and has repeatedly praised schools she sees as serving high-needs students well, such as Broome Street Academy, or have creative approaches, like Voice Charter School.

The schools Fariña visited Monday had invited the chancellor and were starting their school years on Monday, a week before district school students return. Charter schools, which serve a smaller share of English learners and students with disabilities than district schools do, also have more flexibility around how they hire, fire, and pay teachers, and the school day at Girls Prep is eight hours on most days, compared to 6.5 hours for district schools.

As she wrapped up her tour of Girls Prep, Fariña said those freedoms were not the critical ingredients of a thriving school.

“It’s not about how many days or how many hours,” Fariña told reporters in the lobby of Girls Prep, which shares a building with M.S. 302, a district-run school. “It really is about what we do with the time we have in school.”

Charter schools will enroll about 97,000 New York City students this year, or close to 10 percent of the city’s public-school students, up from just 2,400 students in 2003. This year, Fariña will have to contend with another round of requests from new and growing charter schools to share space with district schools — which are often protested by district schools — and an ongoing campaign against low-performing district schools supported by charter schools and their backers.

Fariña said it was important that district and charter schools work together, and told Principal Josie Carbone that she might be able to arrange for other visitors. After seeing that one of the classrooms was named after Supreme Court Justice Sonia Sotomayor, a product of Bronx public schools, Fariña said she’d recently had lunch with her.

“We write her every year,” Carbone told the chancellor, “so if you can get her to come and visit us, we’d love to see her.”