DALLAS (AP) _ An assistant principal is under investigation for gagging an 8-year-old girl and binding her wrists with masking tape as punishment for acting up in class, police said.

The official at Onesimo Hernandez Elementary School was placed on leave when her boss, the principal, spotted the bound girl in a classroom Monday and called police.

The assistant principal, who wasn't identified, acknowledged the discipline was wrong, according to a police report. But she said the girl's mother had instructed her to ``use whatever discipline is necessary to keep my child in line,'' the report said.

The assistant principal is under investigation by police and school officials but had not been charged by Thursday.

The girl's mother told The Dallas Morning News that the taping took place in the presence of other students after she spoke out of turn and struck another child in class.

``I told her to discipline her, but I didn't say she could tape her like that,'' said the mother, who wasn't named to protect the girl's identity.