Last fall, Boston Public Schools Superintendent Brenda Cassellius unveiled a five-year plan to have full-time libraries in every Boston school by 2026. That more than half of the city’s public campuses don’t have such a fundamental facility is surprising, but at least Cassellius was publicly committed to rectifying this shameful deficit. Each of the district’s 125 schools would have a library “unless you’re right next to’’ a Boston Public Library, Cassellius told the School Committee.

Then earlier this month, Cassellius abruptly announced her resignation, effective in June.

Other than naming a police commissioner, there is arguably no more important decision made by the city than choosing a school superintendent. And whoever the Boston School Committee taps for a job that’s been a revolving door, with three superintendents in the past eight years, will arrive to an overflowing inbox. Buildings are in disrepair. Enrollment is dropping. The district’s school bus system is as expensive as it is erratic. Absenteeism, which soared during the pandemic’s remote learning misadventure, continues to plague the district. And too many students are graduating without the tools necessary to foster success for the next chapters of their young lives.

Yet following through with Cassellius’s plan for school libraries must also remain a priority.

In 2019-20, Boston had one full-time librarian for every 6,700 students, according to data from the National Center for Education Statistics. Yet just across the Charles River, there’s one full-time librarian for every 295 Cambridge students. Statistics in Springfield and Worcester aren’t as enviable as those in Cambridge, but each city is still doing significantly better than Boston.

That disparity can have a detrimental impact on students. A 2019 New York State Library study on the “Roles of the School Librarian’’ found that a librarian “empowers learners to become critical thinkers, enthusiastic readers, skillful researchers, and ethical users of information.’’

To keep school libraries viable, recruitment and retention of librarians is crucial. In a recent Boston Globe report, Keith Curry Lance, a consultant with Colorado-based RSL Research Group, said that when school budgets decrease, librarians can be seen as expendable.

“After they eliminate a librarian, the collection becomes hopelessly outdated, and then they eliminate the library because they need the space,’’ he said. “At that point it becomes very expensive to reverse.’’

In a city that touts itself as a beacon of academic excellence, a school library is not a luxury. It is a vital and irreplaceable part of a child’s educational experience beyond the classroom. Nestled among shelves of books, a child can find windows to other lives and worlds. A library is a place where kids can learn, but also develop a love of books and find refuge in them. They can also find themselves.

This is not a minor undertaking. Hiring the best and brightest librarians also means finding those who have a deep knowledge of technologies unheard of the last time Boston’s full-time school libraries were in ample supply.

For too long libraries have seemed an afterthought in Boston schools. This harms students, especially those who might not otherwise have regular access to books. Libraries are integral to learning, and Cassellius’s idea to restore them to full-time status in every school by 2026 is sorely needed. In their search for the next superintendent, Mayor Michelle Wu and the School Committee must get from each candidate a commitment and viable plan to ensure that Boston’s schoolchildren have access to a service that has been overlooked too long.

Editorials represent the views of the Boston Globe Editorial Board. Follow us on Twitter at @GlobeOpinion.