The boy and classmates were disassembling the structure with a teacher.
The 17-year-old's mother later took him to a hospital where doctors found a fractured pelvis and spine, a ruptured urethra, and numerous cuts and abrasions.
Police say the boy's mother was notified that her son had been hurt about 15 minutes after the incident at the county's Assunpink Vo-Tech Center in Hamilton Monday.
Superintendent Kimberly Schneider tells The Times of Trenton the district is meeting with staff to review protocol.
The boy remains hospitalized in serious condition.
Information from: The Times, http://www.nj.com/times
