The latest in a string of teen overdose deaths in the state has prompted lawmakers to call for schools to expand their drug education programs. A 16-year-old Texas girl died of fentanyl poisoning after taking just one pill laced with the opioid, according to her parents and the teen’s school district, who made the announcement on Wednesday.

According to the girl’s family, Sienna Vaughn, a junior at Plano High School in Plano, Texas, swallowed a pill on February 19 that she thought was Percocet, a prescription medication she felt could help her relax. But when Sienna Vaughn’s mother, Stephanie Vaughn, went to check on the two of them, she discovered her daughter to be pale and the friend to be gurgling on the bed, she told KDFW.

Medics rushed the two to a hospital. The friend survived, but Sienna was pronounced dead of what was confirmed to be fentanyl poisoning.

“They didn’t know what they had,” Sienna’s mother told the TV station. “They didn’t know it was fentanyl.”

In a letter sent to parents Wednesday evening, Plano Independent School District Superintendent Theresa Williams confirmed that an unidentified student had recently died of a fentanyl overdose.

“We recently experienced the tragic loss of one of our beloved Plano ISD students to a deadly fentanyl poisoning,” Williams said in the letter, according to WFAA. “I cannot express the sadness and grief that we are all feeling.”

The Vaughn family told The Washington Post that they have been “crushed by the sudden loss of our wonderful daughter and sister.”

Sienna’s death is the most recent tragic teen fentanyl overdose to shake Texas in recent months. In response, parents, lawmakers, and authorities have conducted interviews, suggested legislation, and even put photographs of dead children’s faces on billboards.

Between September and the beginning of March, there have been about a dozen instances of kids in the Carrollton-Farmers Branch Independent School District in North Texas overdosing on fentanyl, according to NBC News. According to a federal complaint filed last month, the incidents, which involve three fatalities, resulted in accusations against three people for conspiracy to distribute and possession with intent to distribute a prohibited narcotic.