New York City would not seem the ideal place at the moment for charter school networks to talk expansion.

Last week, the mayor nixed plans for three charter schools to move into public buildings, and it seems clear that the well of free public-school space that enabled the number of charter schools to mushroom under the previous administration has all but dried up.

And yet, leaders from 11 small but growing charter school networks in New Orleans, Minneapolis, Nashville, Detroit and elsewhere traveled to the city this week to gather expansion advice from Achievement First, a network with 25 schools in New York and other states, and to visit Success Academy, the network who had expansion plans cancelled by the city last week. (Both Achievement First and Success Academy also had public space-sharing plans that the city allowed to proceed.)

The leaders are part of a new program where Achievement First and two other large charter school organizations — YES Prep in Texas and Aspire Public Schools in California and Tennessee — will share lessons with much smaller organizations about how to run and grow charter networks.

During six sessions spread over 18 months, CEOs and other senior leaders from the smaller networks will get tips on how to train teachers, analyze data, balance budgets, and more. In the inaugural session this week, the focus was on developing school leaders and adapting instruction to meet the new Common Core standards.

Paige MacLean, Achievement First’s senior director for strategic partnerships, said the program was planned long before the election of Mayor Bill de Blasio, who has pledged to reign in charter school growth in the city.

MacLean said that some of the largest charter networks — including Uncommon Schools, KIPP, and Success Academy — have long shared best practices, but there had been less collaboration with smaller and newer networks. The training program, called the Charter Network Accelerator, is not meant to “grow little Achievement Firsts,” but to help the smaller networks scale up successfully, MacLean said.

“There is a huge demand for strong networks around the country to open more schools,” she said. “People can’t grow quality schools fast enough.”

Another purpose of the program, which received startup funding from the Gates Foundation, is to foster diversity among charter school leaders. Seven of the 11 CEOs in the program this year are people of color.

“We wanted to address the fact that the prominent leadership of the ed reform movement right now doesn’t ethnically, racially look like the kids that we’re serving,” MacLean added.

In between training sessions Wednesday where an Achievement First CEO described the 25-school network’s rocky transition to the Common Core and shared lessons learned from Success Academy, which did better than most on new standards-aligned tests, one trainee said the advice was welcome.

“Traveling outside the state and seeing other networks who have been doing this longer provides some perspective about what we can be,” said Amy Hunter, the math specialist for LEAD Public Schools, a network of five charters in Nashville.

The discussion Wednesday did not touch on the political opposition charters can face — including in New York City, where concerns that some charter schools serve a select group of students and divert resources from district schools spurred de Blasio to promise new restrictions on them.

But Ian Rowe, CEO of Public Prep, the only New York-based network in the Accelerator program, said that charter and district schools actually work with the same student populations and could learn much from one another.

“I’d love to be in a position where we’re sharing best practices not only among public charter networks,” Rowe said, “but also among public schools.”