"He was my tutor, and he was the nicest kid I've probably known," said student Jack Finnerty.
Like many students at Thousand Oaks High School, Finnerty was in tears and wearing black to mourn the loss of the senior honor student.
Authorities said a hobby rocket exploded on the basketball courts at Madrona Elementary School at about 7:30 p.m. Monday. Moon was rushed to a local hospital, where he later died.
A 17-year-old was also taken to the hospital with minor injuries, deputies said.
Our hearts are broken. But the bonds of faculty, staff, & students will bring healing. Thank you to all for your support at this time.— Thousand Oaks HS (@ThousandOaksHS) April 5, 2016
The teens were making rockets when a propane cylinder tank they were using exploded, according to fire officials. A nurse at the scene was able to start treatment immediately while EMS crews headed to the school.
Finnerty said Moon was working on a science project with a friend.
A meeting was being held at the school for the Boy Scouts and Girl Scouts at the time of the explosion.
"Nobody could really discern what it really was because it was a huge explosion, but it was just all at once. Just a 'boom!' That was it," Tammy Coburn, who was in the meeting, explained.
Ventura County sheriff's officials were investigating the incident. Madrona Elementary School was closed Tuesday due to the investigation.