Rosa Hernandez got the distressing news last month from Arlington's Randolph Elementary School. Her 10-year-old son and another fifth-grader had put soap in their teacher's water bottle, school officials told her.

Although her son insisted he didn't do it, the principal suspended the boys for three days, put them to work cleaning the school cafeteria and had them write statements about what had happened. The teacher wasn't hurt, and Hernandez thought that would be the end of it.

But tomorrow, the case of the soapy drink will move from the principal's office to a juvenile courtroom. The two boys have been charged with a felony: trying to kill or injure the teacher by adulterating his drinking water.

"We're investigating it as a legitimate attempt to make the teacher sick, not simply a prank," said Cpl. Justin McNaull, an Arlington police spokesman. "He recognized that his water tasted wrong and also found a bottle of antibacterial solution near the water."

Patricia Yurrita, an advocate for Hispanic parents in Arlington, said that authorities have overreacted by bringing criminal charges against the two boys and that the case has been very upsetting for Hernandez, an immigrant from El Salvador who speaks little English.

"She's very worried that her son, being such a small child, will be placed in a jail or program," Yurrita said. "To send a 10-year-old to jail--that's ridiculous."

Arlington school spokeswoman Lisa Farbstein said it was the teacher, not school officials, who reported the incident to police.

"It is the teacher who is pursuing this, not the school," Farbstein said. "The teacher called the police, and the teacher has the right to go to police, especially if he feels that alarmed or threatened or violated."

However, she added, "It is not something the school system has encouraged or would have pursued to this level. It sounds like a felony [charge] seems very extreme."

The teacher, named in the juvenile petition as Michael D. Searles, did not return a reporter's telephone call.

The Washington Post is not naming Hernandez's son because of its policy not to identify juvenile defendants.

According to a law enforcement source, police investigating the case were told by other students that the two boys had made statements to their classmates that they hated their teacher and wanted to harm him.

In an interview Friday night at his Arlington apartment, at which his mother was present, Hernandez's son said it was the other boy who put soap in the teacher's water.

But he said he was there when it happened at the end of the school day.

"He didn't like the teacher because he was always sending him to the office," the 10-year-old said of his friend, as Yurrita helped translate. The friend "sits with girls and talks too much," the child said. The other boy's identity could not be learned yesterday.

Holding his fingers about an inch apart, Hernandez's son said that his friend put "like this much" soap in his teacher's water bottle, which was sitting on the desk. The teacher had left the room, and no one else was around, the boy said.

Farbstein said it is not unusual to have soap dispensers in classrooms because school officials have encouraged students to wash their hands often, especially during cold and flu season.

School officials said they did not know what kind of soap was involved, and police would not elaborate. In general, soaps and detergents can cause nausea and vomiting if ingested, said a medical toxicologist with the National Capital Poison Center, and a very potent soap could cause burns.

The felony charge against the two boys would carry a maximum penalty of 20 years in prison if the defendants were adults, but there are no such sentencing guidelines in juvenile cases.

As tears rolled down his cheeks, Hernandez's son said he is worried about what will happen to him now.

"He's just a child," Yurrita said. "He feels very, very bad."

Staff writer Sylvia Moreno contributed to this report.