Quincy officials said the construction of the $50 million Central Middle School off Hancock Street is on track to be completed by Sept. 5. “The brick on the classroom portion of the building is going up now and a lot of work is being done and completed in the interior of the classroom wing,” said Christopher Walker, spokesman for Mayor Thomas Koch. “Classrooms and hallways have taken shape, offices have taken shape, the guts of the building in that portion are well underway, and that process will move to the other section of the building.” Walker said the reaction from the public has been overwhelmingly positive. “People driving by the site remark at how handsome the structure is, even in its skeletal form, and how much presence it will have at the heart of the city,” Walker said. “The community has waited a half-century for [this], so it’s something a lot of people are looking forward to seeing completed.” The city plans to sell the former school property, also on Hancock Street, once the new building is complete.