More than 100 parents, teachers, students and local elected officials crowded the sidewalk outside Brooklyn’s IS 96 Seth Low on March 7 to angrily protest Mayor Bill de Blasio’s decision to go ahead with co-locating a Success Academy charter school in their school building in September.

“We are hugely, hugely disappointed with this decision,” said Laurie Windsor, the president of the District 20 Community Education Council, at the afternoon rally outside the Bensonhurst school. “We were blindsided by this.”

District 21 CEC President Heather Fiorica stressed that the protesters were not opposed to charter schools, only to co-locating them in public school buildings. “Traditional schools should be allowed to grow,” she said.

The parent leaders said the A-rated middle school, which is on the border of Districts 20 and 21, will have to give up its entire fourth floor and share common space including the cafeteria, library and auditorium with 600 K-4 students. The co-location, they charge, will leave no space to meet the mandated testing modifications that must be provided for its large population of English language learners and students with disabilities.

Chapter Leader Sokol Muja said he fears that the co-location puts in jeopardy all the work that has gone into restructuring school programs to offer 13 electives, a project with Maimonides Hospital and a Saturday enrichment program that attracts 60 percent of the students. He also noted that no one from the Success Academy network had shown up at any of the public meetings held to consider the impact of the co-location.

“Don’t interfere with the good work we’ve done as an A-rated school,” Muja urged.

The CEC presidents worried that putting 600 young children in the IS 96 building will mean fewer available seats for the students from the elementary schools that feed into IS 96, a concern compounded by the mayor’s green light for another K-4 charter school co-location at neighboring IS 281. Both targeted middle schools serve students from the two crowded districts, which have added five new elementary schools in the last few years.

“Where are these children all going to go?” Windsor asked. “We need seats for them.”

A day after the rally, Public Advocate Letitia James announced that she and parent leaders were proceeding with a lawsuit against Mayor de Blasio seeking to undo 40 co-locations planned for September 2014, including the one involving IS 96, that were approved in the waning months of the Bloomberg administration and given the green light on Feb. 28 by the mayor.