The expansion will allow the school to take an additional 300 to 400 children.
The mayor has announced new school projects each day this week despite a budget deficit and the closing of nearly 50 schools. He says the Payton project will be paid with tax increment financing money.
"It is in our interest that every child that has the potential to get into a selective enrollment school should not be rejected," Chicago Mayor Rahm Emanuel said.
"There needs to be a solution like a TIFsurplus declared so that all schools benefit, all schools have resources," Jackson Potter, Chicago Teachers Union, said.
The mayor says this is about giving parents choices. He calls the expansion the "right thing" to do.