The second of two Arlington 10-year-olds charged with felonies for putting antibacterial soap in their teacher's drinking water pleaded guilty yesterday to a reduced charge.

The Randolph Elementary School fifth-grader pleaded guilty to misdemeanor assault and battery, said John Whitehead, president of Rutherford Institute, which helped the boy find a lawyer. Sources confirmed the guilty plea. The other boy admitted to the same charge at a hearing last month.

The boy who entered yesterday's plea will be sentenced Feb. 29. Although juvenile court judges have discretion in sentencing, youths convicted of misdemeanor assault are rarely sent to a detention facility. Probation and counseling are common.

"Hopefully it will carry a suspended sentence that will [eventually] be erased from the child's record," Whitehead said. "We were most concerned about making sure this child won't have a record and that common sense would prevail."

The boy's attorney, Patrick N. Anderson, could not be reached. It remained unclear yesterday why the parents of the two boys decided not to go to trial. Deputy Commonwealth's Attorney Theo Stamos said she could not comment because the juvenile court judge in charge of the case has ordered the lawyers and the boys' families not to discuss the case with the media.

Richard J. McCue, the attorney for the boy who pleaded guilty in December, said he is still covered by the gag order because the child has not been sentenced.

The case has sparked controversy because both boys were originally charged with trying to kill or injure their teacher, Michael D. Searles, by "adulterating" his drinking water, a felony. Police said they squirted an alcohol-based antibacterial solution into the teacher's water bottle.

Some parents and educators have said Searles, who was not injured, overreacted by pursuing criminal charges. School officials had already suspended the boys for three days and ordered them to perform community service.

Hispanic parents and activists have been particularly concerned about the case because both children are Hispanic.

"As a mother of three kids, I am shocked to see that in the United States of America, children should be treated this way," said Patricia Yurrita, an advocate for Hispanic parents in Arlington. "It shouldn't have gone that far. Someone who is 10 years old should not go through this experience."

Searles has declined to comment. Law enforcement sources have said other students told investigators that the two boys made threats against the teacher and had plotted to harm him before the Oct. 12 incident.