A few weeks ago, the parent-teacher association at Medgar Evers College Preparatory School — a high-performing public school in Crown Heights, Brooklyn — caught wind of a plan that alarmed them.

The education department intended to seize control of the selective admissions process at the school and begin admitting more disadvantaged students, the PTA believed. It was only a matter of time, the group concluded, before the school would be forced to ratchet down its rigorous curriculum to accommodate the new students — in the process, they feared, undermining a successful, largely African American institution that has long been considered a neighborhood jewel.

The group dashed off a press release warning that officials planned to “dismantle” the school. (On Saturday, a state lawmaker who represents Crown Heights echoed that language in an op-ed opposing the plan, which he called “misguided and flawed.”) On Facebook, community members angrily noted that the city was trying to diversify a high-achieving predominantly black school, even as elite high schools like Stuyvesant remain overwhelmingly white and Asian.

When the PTA called an emergency meeting in the school’s cafeteria this month, hundreds of anxious parents attended. On Wednesday, the group staged a rally against the admissions changes that drew several elected officials.

“The educational aspect of our school will deteriorate” if the city takes over the school’s admissions, PTA President Norelda Cotterel told Chalkbeat last week. “It’s not going to be the same.”

In fact, the proposed changes are not as drastic as those feared by the PTA, education department officials say: By and large, the school will still get to choose whom to admit. But the city will oversee part of the admissions process, and the school will be expected to enroll more students with disabilities, as the Wall Street Journal first reported.

The education department is also imposing the new admissions requirements on other elite city schools, as part of a broader effort to standardize the admissions process and to spread students of different backgrounds and academic levels more evenly across the city’s schools, which are highly segregated by race, class, and academic achievement.

As a result of this campaign, high schools with selective admissions offered seats to three times as many students with disabilities in 2017 as they did five years earlier, according to the education department. Now, the city is setting its sights on the small number of middle schools — including Medgar Evers, which includes grades 6 to 12 — that run their own admissions systems rather than letting students use the city’s standard application form.

So far, this drive to diversify selective schools has centered on students with disabilities. But in the “diversity plan” the city released in June after persistent pressure from advocates, the education department also promised to eventually make selective schools enroll more students “with special instructional or support needs,” including those who are homeless or still learning English.

That goal has left Mayor Bill de Blasio’s administration in a conundrum, underscored by the parents at Medgar Evers: Can the district promote school diversity while at the same time allowing students to be sorted into different schools according to academic achievement or artistic talent?

Some integration advocates say no and have called for the elimination of selective admissions, which is practiced in a quarter of New York City middle schools and a third of high schools. But many parents insist that high-achieving students can be pushed to reach their full potential only when surrounded by similarly strong classmates — a sentiment that has fueled the uproar at Medgar Evers.

Shawana Henry, whose daughter Madison is in the sixth grade at Medgar Evers, said she would gladly have the school enroll more disadvantaged students and ones with disabilities — as long as the coursework remains the same. Yet she also considers the school’s selectivity a vital component of its success.

“Changing the admission process would actually go against the legacy that the school has established,” she said in a text message. “There shouldn’t be any changes made to a school that is doing well unless it’s for further advancement.”

Medgar Evers College Prep, named for the slain African American civil-rights activist, complicates the usual critique of selective programs — that they often exclude low-income students of color. Its student body is 88 percent black and 71 percent from low-income families, and it rests in the city’s top academic tier. (Research has shown that grouping high-achieving black and Hispanic students into the same classes can greatly benefit them.)

Last year, the school achieved a 95 percent graduation rate, with 36 graduates leaving with an associate’s degree — the result of an early-college program that former President Obama lauded in a 2009 speech. The school pushes its students hard: They’re required to attend a six-week summer program each year until 10th grade, by which time most have earned all the credits necessary to graduate, according to the review website Insideschools.

But a big part of the school’s success can be traced to its admissions policy.

Administrators review middle-school applicants’ report cards, fourth-grade test scores, attendance records, and evidence of artistic or athletic talent; it also makes them sit for an entrance exam and interview. The result is that most incoming Medgar Evers students arrive with far higher test scores than the city average, do not have disabilities, and are proficient in English (less than one-half of one percent of students qualify as English learners, compared to 10.2 percent in its Brooklyn district).

To bring the school closer in line with its district’s demographics, the city has been sending it more students with disabilities who did not go through the usual application process; under the new proposal, the school will be expected to recruit and admit even more such students. (Currently 6.4 percent of Medgar Evers students have disabilities, versus 17.3 percent of students in its district.)

Parents, however, fear that eventually the school would have to “realign” its curriculum to meet the needs of a broader range of students — a fear that department officials tried to calm last week, in a visit by Deputy Chancellor Dorita Gibson, who insisted that the focus now is only on boosting the school’s share of students with disabilities.

At the same time, the city has a broader goal to standardize admissions for most middle schools so that families can apply to any school using the city’s standard application form — rather than having to apply directly to certain schools. That has fueled their push to incorporate Medgar Evers and the few middle schools that still manage their own admissions into the education department’s central application process.

Some 13 selective middle schools where students previously applied directly to the school — including the Anderson School and the Institute for Collaborative Education, two popular schools in Manhattan that admit students from across the city — are switching to the centralized system this fall. Medgar Evers will make the change next year for students applying to sixth grade (ninth-grade applicants already use the city’s common application form).

Medgar Evers and the other schools will continue to screen and rank their own applicants, but now they will submit their rankings to the enrollment office, which will notify students who have been accepted.

The department says the shift is mainly a technical change to simplify the application process for families. But it will also allow the city to monitor admissions at selective schools — and, perhaps, intervene if schools appear to be excluding certain groups of students.