Mayor Thomas Menino on Thursday signed off on a schedule shift for the group he charged with radically revamping Boston’s student assignment system. The 27-member group, known as the External Advisory Committee, will now have until January to come up with a proposal to present to Superintendent Carol Johnson.

Boston University’s Dean Hardin Coleman, the committee co-chair, said the schedule delay will allow his group to make a “data-driven” decision. Originally, a proposal was expected to emerge before the end of the year, and before Thursday, the committee had been aiming for Dec. 14.

Coleman said experts from Harvard University and the Massachusetts Institute of Technology will work with school officials on more advanced analyses than they’ve been able to provide to date.

For example, Coleman said, if the city goes to a 6-zone model, they will be able to simulate the consequences of such a model and its impact on students’ access to quality schools.

“We’ll be able to see who is going where and why, and make adjustments to the model,” he said after the group met at City Hall on Thursday night.

The current system divides the city into three large zones. School department officials have proposed several maps, ranging from a map with 23 zones to a map with no zones. A separate proposal from an MIT PhD student has also drawn the EAC’s interest, as has a no-zone proposal from City Councillor At-Large John Connolly and several elected officials. The Connolly plan also includes a network of citywide “magnet” schools and allowing parents to enter the school as a group, a practice known as “compacting.”

School department officials are planning to implement a new map in the 2014 school year.

Bill Walczak, a committee member and co-founder of the Codman Square Health Center, said the target for the committee to deliver a final proposal is now mid-January.

But the task remains daunting. “Every time we look at it, it gets more complex,” Walczak said.

The school department is also providing a seemingly never-ending stream of data. “Every time we get some, it begs for more,” Walczak added.

The External Advisory Committee’s next meeting is set for Dec. 6 at City Hall. Another meeting is scheduled for Dec. 13, with a holiday break before the advisory group meets again.

“Together we are building something new that will serve our families for many years to come,” Menino said in a statement. “This close to a successful outcome, I want to ensure the EAC has the time it needs to get it right.”

More information is available at www.bostonschoolchoice.org.