ARVADA, Colo. -- An Arvada woman who had sex and provided alcohol and drugs at teen parties she hosted pleaded guilty in Jefferson County, Colo., Monday.

Silvia Johnson, 40, entered guilty pleas on two counts of sexual assault and nine counts of contributing to the delinquency of a minor.

Johnson hosted weekly parties at her home over the span of a year and admitted having sexual contact with boys 15 to 17 years old, prosecutors said.

According to her arrest affidavit, Johnson said she also provided marijuana, methamphetamines and alcohol to the teens because she wanted to be a "cool mom" and it made her feel like she was "one of the group." She said she was never popular in high school.

The parties took place between October 2003 and October 2004 and involved boys from Arvada West High School.

One 16-year-old boy told police that Johnson performed oral sex on him on two occasions and that they had sex once. Another 16-year-old also told police that Johnson performed oral sex on him when she was engaging in sexual intercourse with another teen, according to the arrest affidavit.

The investigation began when one of the boys told his mother about what happened.

Johnson told Denver television station KMGH earlier that she was going through a difficult period in her life and that she has apologized to the parents of the teens who are connected to the case.

She'll be sentenced at a later date.