The incident happened about an hour after classes were dismissed on Friday.
School and law enforcement officials say no foul play was involved, but they wouldn't discuss further details out of consideration for the family and the ongoing investigation.
A woman who came to offer her support said she knows the boy's mother.
"She's a single parent and she's got four beautiful children, and I believe he was the oldest," she said.
The school district is providing crisis counseling for any families that request it. All school events planned for the weekend have been canceled.
The Associated Press contributed to this report.