Nine people were treated at a hospital for respiratory distress after breathing the fumes on Jan. 24 at Skyview High School.
The Columbian reports that the 14-year-old mixed bleach and ammonia in a container at home and brought it to school. The Clark County sheriff's office says he asked two students to inhale the mix. One of them pushed the container away, causing it to spill on a third student. Others were exposed to the fumes.
Deputy Prosecutor Rick Olson says it was supposed to be a joke.
The boy pleaded guilty Friday to third-degree assault and reckless endangerment. He got another seven days in detention after pleading guilty to selling marijuana in a separate case. He must complete 64 hours of community service.