PASADENA, Texas -

A former Pasadena school teacher has been accused of having sexual relationships with several students.

LaShawn Simmons, 41, was charged with one count of sexual assault of a child under 17-year-old, two counts of engaging in an improper relationship between an educator and a student, one count of online solicitation of a minor and one count of possession of child pornography.

Simmons is a former math teacher at Beverly Hills Intermediate School. She resigned last month in lieu of termination.

Investigators said Simmons had sex with three of the four former students she's accused of having inappropriate relations with. According to court documents, Simmons picked up the boys after school and took them to her southeast Houston apartment.

The alleged sexual encounters took place from January to September 2012, officials said.

The father of an 18-year-old student in Pasadena ISD said school district police called him two months ago to ask for permission to look at his son's cell phone.

The father said police still has his son's phone.  He said his son denied being involved with Simmons.

"To me I think it's better for her to go ahead and turn herself in," said the father. "These are kids. She shouldn't be doing that. Especially a teacher."

"The allegations are very serious," said Dr. Kirk Lewis, superintendent for the Pasadena ISD. "Anytime a teacher violates the trust of a child, it makes it more difficult for the majority of teachers who genuinely care for the safety and well-being of students. We will continue to work together in the Pasadena ISD to provide a safe environment for our children to learn."

Pasadena ISD police sought charges against Simmons after completing a two-month investigation, which followed a complaint from a parent who said she found a sexually explicit message from Simmons on her son's Facebook account.

The complaint was made on Dec. 10, 2012. Simmons was immediately placed on administrative leave without access to students at the school, Pasadena ISD said.

An arrest warrant was issued for Simmons, but she was not in custody as of Tuesday evening. Simmons had been employed as a teacher at Beverly Hills for 14 years.

Anyone with information related to the case is asked to contact the Pasadena ISD Police Department at 713-740-0063.