Mystery surrounds the case of students fainting at a Kiryas Joel middle school that prompted an evacuation.

School officials say three students between the ages of 7 and 13 at United Telemudic Middle School passed out Tuesday. They say three other students fainted on Monday. School officials originally thought carbon monoxide was to blame and the all-boys school was immediately evacuated. Emergency officials took carbon monoxide readings throughout the building, but tests came back negative.

School officials say one child was taken to the hospital after passing out and the others went to their pediatricians. No cause was found for the fainting.