Investigators have ruled out suicide, homicide, an overdose or any foul play.
The school called Zachary's mother when the 15 year old never showed up for school Monday.
The Sheriff's Department is waiting for autopsy results.
Grief counselors were at Columbia High today to help students deal with the sudden loss.
Principal Kyle Miller told KEPR, "Normal as much as possible in the classrooms. We have, with that said, we possibly had 2 or 3 classes that have almost completely emptied out and they're taken the majority of the kids down to the counseling center."
Zachary would have been 16 at the end of this month.