A bitter clash over space has emerged in recent weeks at a beloved New York City school building on Manhattan’s Upper West Side that two programs have shared for the past decade.

It is a battle that reflects events that have caused two of the biggest demographic shifts in New York City’s recent history: the Covid-19 pandemic and the surge of migrants from the southern border.

One of the building’s occupants, Public School 145, has added more than 120 new students as a result of an influx of newcomers. The Department of Education has proposed moving the other, West Prep Academy, which is losing enrollment, into a separate, but antiquated building to make room for its growing neighbor.

The conflict highlights broader fault lines in New York and other large U.S. cities. The country’s public schools have lost more than 1.2 million students since the pandemic began and are facing major budget declines as a result. Urban areas with large numbers of poor families have been hit the hardest. By 2031, enrollment could plunge by another 2.5 million nationwide, in large part because of declining birthrates.

On the flip side, the surge in new migrant families in New York and elsewhere is helping to offset some of those losses in schools that are well positioned to benefit from the influx. But it has prompted questions in some areas about how resources and space are being used and could place communities on divergent paths.

The plan to split P.S. 145 and West Prep Academy has illuminated how painful change can be. A school building is more than a collection of lockers and classrooms. It is often a neighborhood’s heart and the anchor for a village of children and educators.