Michele Cossey, who bought her teenage son an assault rifle that he planned to use to attack Plymouth-Whitemarsh High School, has been sentenced to three months behind bars.

Cossey, 47, of Plymouth Meeting, pleaded guilty in September to endangering the welfare of her 14-year-old son, Dillon, after arming him. He was planning a Columbine-style assault, which authorities headed off in October 2007 after receiving a tip.

Dillon Cossey was sentenced in December 2007 to seven years in a juvenile-treatment facility near Pittsburgh.

Montgomery County Court Judge Richard J. Hodgson also sentenced Michele Cossey to five years' probation. She was taken to the Montgomery County Correctional Facility to begin serving her sentence after the Monday hearing.

- Derrick Nunnally