FOREST GROVE, Ore. — A pair of Oregon school districts were intent on identifying warning signs that students might be contemplating a campus shooting when they stumbled on a threat far more pervasive yet much less discussed — sexual aggression among classmates.

Unsure at first what to do, the districts adapted the same early-intervention approach used to handle potential school shooters: Based on observations or tips, school staff now quietly keep an eye on kids they worry are sexually aggressive. Parents help the school try to understand why their child is acting out. And the school intervenes if behavior threatens to escalate, whether the student is a kindergartener or about to graduate.

This awakening puts the districts at the forefront of grassroots efforts to grapple with a sensitive and complex challenge that U.S. universities already have been forced to confront but elementary and secondary schools have mostly avoided.