In December, City Councilman Brad Lander announced a proposal to reserve a percentage of seats in all District 15 middle schools specifically for low-income students.

Now comes the hard part: hashing out the details of what could ultimately become one of the city’s first district-wide school integration plans.

Lander has asked the district’s Community Education Council, made up of local parents, to cast a vote in support of his idea. But District 15 CEC members made it clear at a meeting on Tuesday that many concerns will have to be addressed before any plan moves forward.

Among the questions raised: What percentage of seats should be reserved for low-income students? Should there also be a ceiling on the percentage of poor students schools can serve? Could transportation be provided to make it easier on families to travel beyond their neighborhood schools?

Ultimately, those details could be the easiest to agree on. Larger questions — such as how to measure whether the initiative is a success and what diversity plans mean for the schools’ screening policies — could prove even more controversial.

“You can make the change and I’m just wondering, then what?” asked CEC member Marci Aronovitz, who nonetheless called the proposal “reasonable.”

District 15 middle schools are well poised for integration, with a student body that is roughly half black or Hispanic, 16 percent Asian and almost 30 percent white. The district’s choice policy, which allows students to apply to any middle school they choose, also increases the opportunity for students to leave their own neighborhoods.

Yet schools in the area are deeply stratified by race and class, with white students mainly attending the district’s three most selective schools — M.S. 51, M.S. 447 and New Voices School of Academic and Creative Arts — and poor students concentrated in others.

The city Department of Education has already allowed 19 schools in Brooklyn and Manhattan to implement “set-asides” for low-income students under its Diversity in Admissions program, which was opened to all city schools last spring.

Even with a suggested 40 percent set-aside, the impact in District 15 is likely to be modest. According to projections shared by Councilman Lander’s office, about 230 more poor students would be enrolled in the district’s three wealthiest schools — M.S. 51, M.S. 447 and M.S. 839. Two of those schools — M.S. 447 and M.S. 839 — have already joined the city’s Diversity in Admissions program and will implement set-asides in the next school year.

Council members agreed that outreach will be crucial if the plan is to work. Without a diverse set of student applicants, the set-asides might not matter.

“How can we really make sure that we can get the word out to the parents?” asked CEC president Naila Rosario.

Superintendent Anita Skop, who recently launched a committee to discuss diversity issues district-wide, said it will also be important to focus on what happens inside schools. To ensure not just numerical diversity but also a culture of inclusion, Skop said she is taking a hard look at issues such as curriculum used in the classroom.

“How do we teach history? Whose story gets told?” she asked. “The way we teach history has to be more inclusive, more diverse. That’s something I, as a superintendent, can encourage.”