Cheryl Hensley, a librarian in Houston, was excited for the start of school. A veteran of four decades in the city’s public school system, she had stocked her library at Lockhart Elementary, a mostly Black school, with $40,000 in new books, and won a statewide award for her work.

Then, late last month, Ms. Hensley, 62, was told she was no longer needed: The school’s library would be one of dozens turned into multipurpose computer rooms and used, in part, for discipline.

The decision to fire librarians and effectively close libraries in some of the city’s poorest schools has been the most contentious yet made by a new set of Houston public school leaders who were imposed on the district and its 187,000 mostly Black and Hispanic students this year by the administration of Gov. Greg Abbott.

The state of Texas this spring took over the Houston Independent School District, one of the nation’s largest school systems, and replaced its elected school board and the superintendent. The move had been years in the making, following chronic poor performance at some schools, past allegations of misconduct by school trustees and changes in state law — backed by a moderate Black Democrat from Houston — that made it easier for the state to take over school districts.

Since then, the new superintendent — a former Army Ranger, State Department diplomat and founder of a charter school network who has no official certification for the Houston job — has moved swiftly to adopt a new plan for educating the district’s children, focusing on rapidly improving reading and math scores in dozens of elementary and middle schools.

“The future is here, and we’re behind,” the superintendent, Mike Miles, said at a community meeting this month, describing persistent achievement gaps between Houston students and others around the state, and between the district’s Black and Hispanic students and their white classmates. “It means we have to do bold things now.