The incident took place April 22 about 15 minutes before the 7 a.m. start to classes, Principal Ron Pritchard said.
Students were gathered outside, as they typically do before the bell rings, and he heard what sounded like a firecracker, he said.
Instead, it was the contents of a water bottle exploding. No one was injured, nor was there any damage, and Kiera told administrators and police she did not intend to hurt anyone or disrupt school.
The police report said Kiera mixed "The Works" toilet bowl cleaner and pieces of aluminum foil in the bottle. She said that a friend told her about the concoction and that she was considering it as a possible science fair experiment, the report noted, but her science teacher said it was not part of any class assignment.
Pritchard said Kiera and students who were nearby could have been injured.
Kiera had no prior discipline problems, Pritchard said. The State Attorney's office said she had no prior criminal history.
Many upset by her arrest viewed it as a sign of school "zero tolerance" policies gone too far.