A driver struck and injured an on-duty crossing guard employed by the Suffolk County Police Department outside a Medford elementary school, officials said.

Suffolk County police said the guard was helping an adult pedestrian cross the intersection at Beechnut and Wave avenues just after 9 a.m. Tuesday, when the driver allegedly failed to yield.

According to investigators, the guard was in the crosswalk and had displayed her stop sign when the collision happened. She was taken to Stony Brook University Hospital for treatment.

The pedestrian being helped by the guard had not yet entered the crosswalk and was uninjured.

The driver, identified by police as Blue Point resident Paulette Nicosia, 67, was issued a summons for failure to yield.