470 school districts in the U.S. have at least one school on a four-day week but a lack of available data means that number could be much higher.
Authorities only learned of the threat through a teacher's husband.
The suspects were detained after entering the school to pick up a friend and charged with second-degree trespassing.
Schools in Oklahoma are looking at bulletproof storm shelters to protect students from deadly tornadoes and the possibility of an active shooter on campus.
A Pittsburgh Public School teacher allegedly was attacked by a parent for confiscating her elementary student's cellphone in class.
Drew Adams, a 16-year-old boy assigned female at birth, says administrators have prevented him from using the boys' restroom.
In 2007, 65 percent of lesbian, gay and bisexual students said they'd been bullied. This year, 45 percent did.