Jeffrey, 41, entered the guilty plea a week before his trial was scheduled to begin, according to CNN.
He was charged in February with solicitation of statutory sexual assault, solicitation of involuntary deviate sexual intercourse, solicitation of child sexual abuse and unlawful contact with a minor, among 14 total charges, PEOPLE confirmed at the time.
University spokeswoman Lisa Powers says the school stopped using Schultz's name shortly after the Sandusky scandal broke.
Sandusky's pleas guarantee that he will serve 3 to 6 years in state incarceration, but it allows the judge in the case to impose as much as 4 to 8 years at her discretion, according to the district attorney's office.
Jerry Sandusky is now serving a prison sentence of at least 30 years from a 2012 conviction for sexually molesting at least 10 boys while at Penn State.
Pennsylvania State Police launched an investigation after the father of the younger girl discovered text exchanges from Sandusky asking for naked photos. Investigators successfully recovered the text messages, confirming the victim's report. She told police she believed Sandusky also had tried to watch her while she was in the shower. Sandusky reportedly first told her he didn't remember what he had said, but later said he knew it was wrong.
His adoptive father, former Penn State football coach Jerry Sandusky, is serving time in prison on his own child sex crime charges.
District Attorney Stacy Parks Miller said prosecutors were prepared to go to trial, but Sandusky pleaded guilty to all the charges.
"We are happy that these girls can move forward and experience a life with adults that deserve their trust", she said.