An eight-year-old Southern California boy has been missing since late Monday morning, when he ran away from school and into a neighboring forest.

San Bernardino County sheriff's spokeswoman Cindy Bachman said that Joshua Robb ran out of the gates of Grandview Elementary School's playground in Arrowhead at about 11 a.m. local time on Monday, outrunning the school staff who chased him.

The boy is severely autistic and does not respond well to loud noises or loud voices, and unfortunately in this situation we have to have the helicopter searching for him so I'm sure that is somewhat disturbing to him but it's absolutely necessary, added Bachman.

Joshua's parents told ABC News in Los Angeles that their son had recently been taken from them and put into the custody of his teacher, after a witness saw him tied to a pole. His parents said they sometimes to do that to restrain him.

All he knows is us. We've never had a break from my son ever since he was born, said his father, Ron Robb. We know for a fact that that's why he escaped, because he was out trying to find us.

There's no word on whether or not the teacher who had custody of Joshua was present when he disappeared.

The weather in the San Bernadino Mountain area hasn't been ideal -- with rain and temperatures down in the 40s. 

Joshua is 60-75 pounds, with brown hair and dark brown eyes. He was last seen wearing a tan and grey-striped collared shirt, black shorts and grey sandals.