The arrest of a Northern California high school teacher for sexual abuse of a 14-year-old male student has raised questions about the boundaries of behavior and whether schools should police social media contact between teachers and students, authorities said on Friday.

Marie Johnson was a popular math teacher at Granada High School in Livermore, which is 35 miles east of San Francisco, and students and staff at the campus expressed shock at the case.

Johnson is charged with unlawful sexual intercourse with a person under 18, oral copulation with a minor and lewd act upon a child. She faces a total of 24 counts of those charges.

Police said Johnson formed a relationship with the unidentified, 14-year-old male student through text messages, Facebook, and the smartphone game Words with Friends.

The sexual assaults reportedly occurred over the course of six months from December 2010 to May 2011 in Johnson's vehicle and other undisclosed locations, the Livermore Police Department said in a statement.

The incident has sparked a conversation in the Livermore Valley Joint Unified School District about the appropriate use of social media and boundaries between students and teachers.

I think this will prompt us to redistribute our policies and go over them with staff, said Assistant Superintendent Chris Van Schaack.

Teachers are prohibited from socializing with students through electronic devices on campus, and discouraged but not banned from doing it on their own time, he said.

But he said a total ban might be counterproductive since some teachers have set up instruction-related Facebook accounts, through which they do not socialize but instead communicate with students about assignments.

We actually think that's good, he said.

Regulating online interactions between educators and students has proved a challenge across the country.

Missouri lawmakers in spring 2011 passed a law that would have prevented teachers and students from communicating privately over the Internet on social media sites such as Facebook. Teachers, the American Civil Liberties Union and other groups objected to the law, with instructors arguing that the vast majority of their online contacts with students were only education-related.

A state court judge later blocked the law from going into effect, and the governor signed a bill that repealed part of the controversial legislation and ordered school districts to come up with their own online communication policies.

Authorities have encouraged parents of Granada High students to ask their children about the nature of any contacts they had with Johnson.

Devon Schandel, 18, a Granada High senior who is friends with Johnson on Facebook, said he was flabbergasted by her arrest. From what I knew about her, she always came across as a kind, caring person who respected her students and was there for them as they needed her, he said.

Police did not return calls asking for comment on Friday. Johnson's lawyer and a district attorney's office spokesperson both declined to comment.