The city released new data Friday about the quality of its rapidly expanded pre-kindergarten program, which officials touted as evidence that the program has maintained high standards even as it enrolled nearly 50,000 additional students over the past two years.

With free full-day preschool as the centerpiece of his education agenda, Mayor Bill de Blasio has more than tripled enrollment since he took office — leaving some observers to wonder whether the city was trading quantity of seats for quality. The new data, compiled from reviews of a portion of the city’s 1,800 pre-K sites that were conducted from 2012 to the present, shows that the quality of New York’s pre-K program is on par with other cities.

The inspected sites on average met or surpassed the national average on a measure of teacher-student interactions, according to review of 555 cites. On a different measure, 77 percent of reviewed sites earned a 3.4 or above on a 7-point scale, which city officials said is the benchmark that programs must reach to have a positive impact on students.

However, Steven Barnett, a professor at Rutgers who is an expert on preschool programs, said that programs should strive to score a five or higher on that scale. The results are promising, he added, but should be seen as a baseline that the city should improve upon.

“They’re OK, but they’re not nearly as good as they should be five years from now,” he said. “It’s not an overnight process.”

Officials also announced that pre-K enrollment reached over 68,500 — just shy of de Blasio’s goal of 70,000 — and said that a recent crop of new students came primarily from low-income backgrounds. Of the 3,000 students who have enrolled since September, 90 percent live in zip codes with incomes below the city’s median.

The pre-K expansion has been one of de Blasio’s only initiatives to garner positive reviews from most observers.

“We’re proud Pre-K for All is performing on a level with some of the most highly-regarded programs in the nation,” de Blasio said in a statement.

The education department used two observation-based measures for the report.

The first, known as the Classroom Assessment Scoring System, focused on how teachers interact with students. It uses smiling and laughter to gauge school climate and judges the quality of questioning in a class. The second, called the Early Childhood Environmental Rating Scale, used room set-up and student hygiene, as well as the quality of instruction.

More than 1,000 pre-K programs were evaluated using the second measure in the past three years. On average, they scored 3.9 on the 7-point scale. City officials said a 3.4 is correlated with “improved student outcomes,” including better reading, math, thinking, and social skills.

Barnett, who has studied New Jersey’s celebrated pre-K expansion, said it’s encouraging that categories like “language” and “interaction” were scored higher than “space and furnishings” or “personal care routines.” That implies physical space and classroom routines weighed down the ratings, not teacher instruction, he said.

New York’s scores align with pre-K programs in other cities. New Jersey’s Abbott program scored a 4.0 on the ECERS-R scale in 2002-03, just 0.1 points higher than New York’s rating.

Not all of the city’s 1,800 pre-K sites were evaluated, but soon the city plans to assess all programs. Every three years, each pre-K program should receive both ratings, city officials said.

City officials said they will direct more resources to pre-K programs with low scores on these measures, including extra social workers or more professional development.

They did not offer any specific plans to close struggling pre-K programs based on these observations, though they said that is a possibility in the future. The officials also said they would consider a site’s scores when considering whether to renew providers’ contracts.

For K-12 schools, the city publishes data in annual progress reports for parents. City officials did not say they plan to present pre-K information in a similar way, though all of the data is available on their website.