New security measures adopted after December’s school shooting in Connecticut are expected to be in place at all of the city’s elementary and middle schools by the end of next month. The district is spending $556,000 to install cameras and buzzers, replace doors, and put in new hardware and electric wiring at the schools, said Superintendent David Fleishman. The new equipment will go into 20 district buildings, including all of the elementary and middle schools, and the administrative center, which houses a preschool and high school program. Much of the work will happen over April vacation. “We’re moving as quickly as possible,” Fleishman said. The tighter security will be a culture change for many Newton parents who are used to open schools, he said. But after the fatal shooting of 20 children and six adults in Newtown, Conn., many parents questioned why the local buildings were left unlocked. Parents will still be able walk into the schools during morning drop-offs, but new procedures will be in place during the school day, Fleishman said.