A D.C. Council hearing room was packed Thursday afternoon with parents, teachers and activists eager to weigh in on Chancellor Kaya Henderson’s plan to close 20 schools across the city.

Council members began the hearing with opening statements, using the opportunity both to praise the chancellor’s efforts to invite community input and raise concerns with her proposal. Mary Cheh (D-Ward 3) said that while the school system needs to deal with its half-filled buildings now, in the future it must be more proactive about figuring out how to attract and keep District families.

“We need a plan that’s forward looking and attempts to save our schools, not wait until things are on a downward spiral and then say we have to close some,” Cheh said.

The plan, announced Tuesday, has already roiled communities and provoked questions about how the city’s traditional public school system will coexist with the District’s fast-growing public charter schools.

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There already have been early tussles about what will become of school buildings left vacant under the plan. Henderson said she would like to retain the facilities in case enrollment rebounds in the future, but some charter-school advocates say the buildings should be turned over to high-performing charters that are desperate for space.

Jack Evans (D-Ward 2) agreed, saying that parents with young children want to know where they will go to elementary, middle and high school. They want a comprehensive plan for creating a stable, strong school system, he said.

“Every parent in every neighborhood is asking for that plan,” Evans said.

Henderson has promised to listen to community feedback and tweak her plan in response to what she hears. But the chancellor, who has the authority to close schools without city council approval, also has made it clear that 20 schools must close.

After decades of dwindling enrollment, she argues, the school system must downsize in order to concentrate resources on improving academic programs instead of operating half-filled buildings.

More than 50 people were scheduled to testify at Thursday’s hearing, the first of several planned public discussions of Henderson’s closure plan. Another 50 are scheduled to testify at a second council hearing Monday, and then the school system will sponsor four community meetings in late November and early December.

Henderson has said she will finalize the closure list by mid-January.

Among the witnesses scheduled to speak Thursday were several parents from Northwest Washington’s Garrison Elementary, which is slated to be shuttered.

With about 228 students, Garrison is operating at about two-thirds capacity. But parents say the school is building momentum, drawing more of the neighborhood’s many young families with the help of a new, energetic principal.

They already have launched an online petition and social media campaign, and they have won support from two council members — Jack Evans (D-Ward 2) and Jim Graham (D-Ward 1) — for keeping the school open.

“We will prove to DCPS that we have strength not only in numbers, but in passion and spirit, and we’ll go down fighting,” PTA officers wrote in an e-mail to their school community.

Under the chancellor’s plan, the closures would displace about 3,000 students, who would be sent to nearby schools with extra space. School system officials said they could not say how many employees might be laid off as a result of the closures.

The Washington Teachers Union has demanded that the school system guarantee jobs for displaced teachers rated effective and highly effective on annual evaluations. School system officials said they would do their best to retain excellent teachers, but stopped short of making any promises.

“One of our bedrock principles is that our school principals need to have the authority to decide who teaches in their buildings,” spokeswoman Melissa Salmanowitz wrote in an e-mail. If teachers can’t find jobs within the system, their union contract gives them one year to continue looking or take a buyout.