The Osakis, Minn., School District is investigating allegations that bullies tied up a high school student with an electrical cord during class while a teacher failed to intervene.

Superintendent Joseph Broderick said the administration and school board "are aware of the allegations of misconduct and … we're going to do our due diligence and investigate it."

On Friday, Nicolette Rochefort posted a picture of her 15-year-old son with his hands tied behind his back and cords wrapped around his neck over a sweatshirt with the black hood scrunched around his face. The boy, a student at Osakis High School, is shown sitting on the floor, with his back hunched and head bent over. Rochefort said she discovered the picture on Snap Chat.

"Bullies did this to my son today at school in a classroom with a teacher present who did nothing about it for 40 minutes," Rochefort wrote in a Facebook post that was shared by more than 16,500 users. "… Bullying policies are NOT working!"

Rochefort said in the post that the bullies were 18 and 17, and told other media outlets that her son had been repeatedly harassed by upperclassmen. Authorities have said they aren't pursuing charges.

Broderick said the school would examine the claims "in a timely manner."

Facebook picture posted by Nicollete Rochefort