A decade ago, Australia nearly topped the charts when it came to teaching children to read. Although Australia has fallen in more recent international rankings, its reputation has helped one company dominate the New York City market in on-the-job teacher training.

It’s a big market.

In total, New York City’s public schools spent about $100 million on training for teachers and principals last year. The top-earning professional development company, Australian United States Services in Education, or AUSSIE, took in more than $15 million in 2011, according to an analysis by The Hechinger Report of a decade’s worth of school spending data.

According to the records, dozens of schools spend more than $70,000 annually, at about $1,000 per day, on AUSSIE consultants, many imported from Australia.

“I was always very impressed with the amount of money that New York City was willing to put into professional learning,” said Diane Snowball, an Australian who co-founded AUSSIE with her husband in 1992. She is now retired and no longer involved with the company.

As the state strengthens accountability measures, principals are looking for ways to help teachers improve their skills. While schools have to prove they are increasing student test scores, the city’s Department of Education doesn’t hold private companies to the same rules. There is little oversight of the money funneled to private consultants, or guidance to help principals figure out which ones help improve student achievement.

In one of its contracts with the city, AUSSIE cites growth on test scores in two Bronx districts and three struggling schools where it has worked. But, as with most providers, there are no independent reviews of AUSSIE’s performance in terms of student test scores or other measures.

Company officials declined to comment for this article.

AUSSIE has spread because it “provided strong coaching to schools,” Josh Thomases, the department’s deputy chief academic officer, said in a statement. Education Department officials say they want principals to decide which providers work best for them.

“We’ve watched organizations that have not done as good a job as we would have hoped or who are new on the scene that have done interesting and exciting work, and have shared that information around,” Mr. Thomases said. “What we’re not willing to do is take away principal discretion.”

The company’s reputation is built mainly on anecdotal evidence, including a successful reform effort in the 1990s in District 2, which encompasses parts of Lower Manhattan and the Upper East Side. Back then, statistics showed that Australians read more books than people in other countries, Ms. Snowball said, and in 2000 the country ranked fourth in the world in reading on the Programme for International Student Assessment, a test taken by 15-year-olds in more than 30 countries. (The United States ranked 15th.)

Ms. Snowball was known in Australia as a literacy expert, so in the early 90s the superintendent of District 2 invited her to train principals and teachers in their approach, which was focused on giving books to students which matched their reading level.

Daria Rigney, a former superintendent who is now a literacy consultant, was a District 2 school principal at the time, and calls the AUSSIE consultants “consummate professionals.” But they were also supposed to be temporary.

“The idea was not to hire AUSSIEs forever and ever, and that they become this external wing of your organization,” Ms. Rigney said. “It was about building the capacity of the people who were the practitioners.”

The company was concentrated in District 2 during the 1990s, but since then AUSSIE consultants have spread from a few dozen schools and Department of Education programs to more than 300. In 2004, the company’s earnings from the system peaked at nearly $30 million, and it has become a permanent fixture at many schools.

Public School 279, a K-through-eighth grade school in the Bronx, has hired AUSSIE consultants nearly every year since 2004, spending a total of about $800,000. Forty percent of fourth graders were proficient on state reading tests last year, but the school has received high marks from the city for its progress.

On a recent morning, Olivia Atanasovska, speaking in a crisp Australian accent, was helping a group of P.S. 279 kindergarten teachers develop a curriculum. Ms. Atanasovska, a teacher for 12 years in Melbourne and a literacy coach for three, says it often takes half the year for teachers to trust her.

“It’s a question a lot of the teachers have asked, too: ‘Why an Australian?’ ” she said.

AUSSIE doesn’t focus on just reading anymore, but will customize its training to whatever a school principal wants, whether it’s analyzing data or helping teachers learn new standards. Ms. Atanasovska works with several schools, most in the Bronx. During her weekly visits, she, among other things, meets with administrators, observes classrooms, and facilitates meetings among teachers.

P.S. 279 is reliant on AUSSIE for several reasons, said its principal, James Waslawski. He has a high turnover of teachers at his overcrowded, high-poverty school, meaning frequent training sessions for the new hires. He used to rely on administrators within the school system to help with training, but that changed after the former chancellor Joel Klein dismantled the old bureaucracy, Mr. Waslawski says. Consultants are “built into the model. They really are,” he says.

For the most part, Mr. Waslawski said he had had good experiences. But he wishes the Education Department would provide more help for principals trying to navigate the growing teacher-training marketplace. “Part of me sort of resents that there’s no filter,” he said.

This story was produced by The Hechinger Report, a nonprofit, nonpartisan education-news outlet based at Teachers College, Columbia University. Jill Barshay contributed reporting.