As President Trump promised mass deportations, educators sounded alarms that the actions could scare families away from school, affecting both immigrant and nonimmigrant students.

Now, new research provides evidence that immigration raids did appear to lower school attendance. A Stanford University study found that parents kept their children out of school more often after raids swept California’s Central Valley this winter.

The findings suggest raids can harm student achievement and disrupt how schools function, even when they do not occur on or near school grounds. The study, by Thomas S. Dee, a professor of education at Stanford University, found that daily absences jumped 22 percent around the time raids occurred.

This week, the administration deployed troops to Los Angeles in response to protests against deportations. Absences went up, even though the district tried to reassure families that schools were safe.

The new paper looked at attendance data from five school districts in the southern part of the Central Valley, serving a total of over 100,000 children. Public schools do not track immigration status. But a majority of students in the region are Latino, many the children of farm workers with uncertain legal status. Those workers help produce about a quarter of the nation’s food — fruits, vegetables, grains and nuts.

Professor Dee examined three years of attendance data. He found an unusual spike in absences this past January and February following “Operation Return to Sender,” a series of immigration sweeps conducted by U.S. Customs and Border Protection.