Plano ISD officials are warning parents about a dangerous game that some students may be playing.
Students playing the "fainting game" are intentionally cutting off their oxygen supply for a temporary high.
The game could result in brain damage, seizures, stroke and even death.
In a letter sent home to parents, the district says parents should look for frequent headaches, broken blood vessels in the eyes, and marks on the neck.
The district says children who play the "fainting game" are typically between 9 and 16 years old and are motivated by curiosity, not depression or anger.
The district didn't say if a specific incident prompted the letter.