Parents in Williamsbridge say they are on edge after a man allegedly tried to sexually assault an 11-year-old boy.

Police say the boy was grabbed from behind in the middle of the afternoon by a stranger at the corner of White Plains Road and Magenta Avenue. They say the suspect pulled out a knife and told the boy to follow him to a park.

Once there, police say the assailant punched the 11-year-old in the face and then pulled down his pants and tried to sexually assault him. They say the boy was able to get away after fighting off his attacker.

Parents at P.S. 41 passed around a letter Thursday morning that was sent home by the elementary school informing them about the incident, which police have classified as an attempted criminal sex act.

In the letter, the school says it's now providing extra school safety agents during dismissal and is reminding parents to review safety measures with their children.

Many parents tell News 12 more needs to be done to catch the alleged predator.

The suspect is described as a thin light-skinned black man between 17 to 19 years old. He was last seen wearing a blue hoodie and white and blue Air Jordans.  

Anyone with information is asked to contact police.