The Pinal County Sheriff's Office arrested a 15-year-old ninth-grader accused of bringing a soda bottle filled with drain cleaner to a Queen Creek-area school after the bottle burst and injured him and eight other children.

Sheriff's spokeswoman Lt. Tamatha Villar said the teenager told investigators he has been practicing building such devices with different chemicals and reactive agents to see what happened.

The suspect, whose name was not released, was being held Monday night at a juvenile detention facility on suspicion of aggravated assault, disorderly conduct, disruption of an educational institution, and disposal of an explosive device. Villar said that the teen didn't offer a motive to investigators.

�There's no reason for us to believe his intent was to blow up the school or cause the mass damage,� she said.

The incident unfolded at 8 a.m. Monday at J.O. Combs Middle School in Pinal County and led to two children being taken to a hospital by ambulance as a precaution; others were taken to hospitals by their parents. Authorities said at least four children were treated and released by late afternoon.

A total of six boys and three girls suffered what were described as minor-to-moderate injuries that included burns to their hands, faces, and arms.

Villar said that one girl appeared to have suffered burns to the eyes. District officials said staff members first thought the bottle had been filled with vinegar and baking soda, because students had been using that mixture in recent science experiments.

But Steve Henry, chief sheriff's deputy, said the sheriff's office was treating the bottle and mixture as an �improvised explosive device,� or IED, usually a description reserved for deadly homemade explosives used by terrorists.

Meanwhile, a Rural Metro official said the school didn't contact 911 when the explosion occurred and instead had the children take showers. Rural Metro was finally notified about 2� hours later.

�We were never called for the explosion. We should have been,� said Bill Grubb, deputy fire chief for Rural Metro. �The call didn't evolve right. Somebody made a mistake.�

District officials said school staff called poison control and followed directions on how to treat the students, which �provided the students with temporary relief,� according to a prepared statement.

Paramedics were called later when the students again complained of �some discomfort.� The statement said school officials were still investigating the incident.

�Poison control was good, but 911 would have been ideal,� Villar said.

Combs eighth-grader Courtney Borseth said she saw one female victim after she had taken a shower. �She had red all over her arms,� she said.

About 1,000 students were locked down in their classrooms while officials looked for additional explosives and a HAZMAT crew cleared the area. Early Monday afternoon, the students were bused to the district office at Combs and Gantzel roads, where parents were asked to pick them up.

Some parents who showed up at the school after being notified of the incident by phone said they were upset and faulted district officials for a lack of security at the school.

Staff writer Emily Gersema and the Associated Press contributed to this report.