A New York City teenager was fatally struck while walking along a state parkway on Long Island after leaving his school for exceptional children by himself, the boy's family said. 

New York State Police said 15-year-old Christopher Williams was hit by a car Thursday afternoon on the Southern State Parkway in Valley Stream.

He was pronounced dead at a hospital after the accident near Exit 13, about a half-mile from The Martin De Porres School for Exceptional Children, police said. 

Special needs teen left school unsupervised, family says

Williams' family in St. Albans, Queens, said he was a special needs student at the school in Elmont and somehow left unsupervised before the accident. 

"On what should have been a normal school day, our world was shattered forever. The school failed him, and now our family is left with an unimaginable loss. A bright light that is now lost forever," the boy's brother wrote in a text message to CBS News New York. 

According to Williams' mother, the school called her and asked where her son was before police summoned the family to identify his body. 

The Martin De Porres School released a statement Friday saying the community "is heartbroken at the loss of one of our students, and our entire community is grieving today. We extend our deepest condolences to the student's family, friends, and loved ones. Counseling and support services are being made available to our students and staff, and we ask for privacy so our school community can grieve and begin the healing process."

A group is raising money to help Williams' family pay for his funeral. 

State police are investigating the crash.  

School conducting "a top-down review"

Joe Trainor, executive director of the school, said in the statement that a full review of the school's policies and procedures was underway after the student's death. 

"The mission of The Martin De Porres is to educate children experiencing emotional and behavioral problems, and through that education, we strive for every child to have the opportunity to reach his or her fullest potential. We will always stay true to those core values and put the health and education of our children first. As such, we take this incident very seriously and, working with our board, have already begun a top-down review of our internal procedures and policies," Trainor said. 

Parents in the school community want their questions answered promptly. 

"The fact that the child even got that far is really scary. Where is the security at the school and the teachers?" Tiaba Lubin said. 

"Very unsafe. I think the school would have to be responsible. Doesn't make any sense for a child with special needs to get out of the school," Marie Senville said. 

Kindergartener leaves school after jumping fence

The day before Williams' death, another Long Island special needs student walked home from school alone after climbing a fence. 

Rockville Centre parents attended a school board meeting after the superintendent said a 5-year-old kindergartener with autism left Riverside Elementary School while they and other students were in the playground area Wednesday. 

The neighborhood is adjacent to the Mill River, which has danger signs posted around it. 

Police said school officials notified them that the child was missing before they were found safe at home about 30 minutes later. 

The superintendent told parents that a review was underway to retrain staff and review the security of the school's fences and gates.