For the second time in two days, a Nassau County student was able to walk off of a school campus. This time, it ended in tragedy.

Christopher Williams, 15, died Thursday afternoon when he was struck by a car as he was walking along the Southern State Parkway near Exit 13 in Valley Stream. New York State Police said the driver was going eastbound around 1:15 p.m.

The teen from St. Albans, Queens, was taken to Long Island Jewish Valley Stream, where he died.

"No one laid eyes on him when this was happening," Christopher's brother Dealza Lewis said. "No one was able to stop him from doing this and now, I'm never going to see him again, so I don't think they did a good job."

Moments before the tragedy, Williams was reported missing from the Martin de Porres School for Exceptional Children, a special needs school in Elmont, less than a mile from the crash.

It's not clear how the boy was able to get off school grounds or how he ended up on the parkway.

In a statement to News 12, Martin De Porres School for Exceptional Children Executive Director Joe Trainor said: "The Martin De Porres family 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. 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.”

In a GoFundMe page for the victim, the family claims the school called the teen's mother asking where he was, unaware that Williams was already gone.

"He was only 15 years old, with his whole life ahead of him," the family shared online. "The school failed him, and now our family is left grieving an unimaginable loss."

The tragedy comes one day after a Rockville Centre Kindergartner was able to climb a fence during an outdoor activity at Riverside Elementary School and leave school grounds. The 5-year-old's family said the child with autism walked half a mile from the school to his home, where first responders found him safely after the school district placed a 911 call about a missing student.

In response, the Rockville Centre School District said it was reviewing all of its security policies.

Williams' family said his mother does not have the money to cover his funeral expenses and is hoping to raise the funds necessary.