Each of the city’s 32 community school districts will determine its own middle school admissions policies, and selective high schools will use a new admissions system that will give top preference to students scoring in the top 15% of their school or citywide, Schools Chancellor David Banks announced Thursday.

There will be no changes to specialized high school admissions — the eight schools, including Stuyvesant and Brooklyn Tech — that use the state-mandated Specialized High Schools Admission Test or SHSAT as their sole basis for admissions.

The new policies come just weeks ahead of the opening of middle- and high-school applications, a fraught process for public school students, who in many parts of the city are typically not zoned for a neighborhood high school, and instead must rank 12 high school choices in order of their preference.

Some of those schools use simple lotteries if there are more applicants than seats, but others, called screened high schools, judge students on criteria like state tests scores and classroom grades.

In the past, those schools admitted students by simply ranking them, top-down - a process that often left some of the city’s most sought-after high schools less diverse than the school system at large. Last year, the de Blasio administration rolled out a new policy: all students whose grades averaged out to about an 85 or higher were put into the same pool of applicants, and then selected by a lottery.

The new policy for screened schools will admit children in group order. Group one will be composed of students whose seventh-grade course grades fall in the highest 15% of their school, or the highest 15% citywide, as long as the average is at least a 90.

Group two will be students who did not make group one, but are in the top 30% of their school or citywide, with an average of at least an 80. Group three will be students who did not make group one or two, but are in the top 50% of students in their school or citywide, with an average of at least 70.

Students in group one have the top priority - and group two will only be admitted if all students in group one are accommodated, the city says.

Applications to high schools will open on October 12.

At the middle-school level, it will be up to superintendents of each of the city’s 32 geographic districts to determine whether middle schools will used screened admissions - and what those screens will be. Superintendents will decide after engaging the community, city officials say.

There’s not much time to settle on a system. Middle-school admissions open on October 26.

The city is also hoping to make the process -famously byzantine - a little simpler. This year’s applications are opening earlier than last year, and students will get their high school offers in March, and middle school offers in April. That’s much earlier than last year, when students did not get their high school offers until well into June.

There will also be a streamlined calendar for open houses held at schools, and clearer information will be provided about the chances of getting into a particular school or program. The city will also extend wait lists for schools into mid-September next year, to ensure any open seats get filled fairly.