The Long Island school year has gotten off to a scary start for parents and students, as at least three districts say they have dealt with threats or weapons brought to school.

The Sachem Central School District says a Sachem High School North student brought a knife Thursday onto a school bus.

A letter from District Superintendent Patricia Trombetta says the student showed the knife to another student at the bus stop.

The district says another student alerted staff and that police were called.

Suffolk County police say they are investigating the incident.

A student brought a bullet to Jonas E. Salk Middle School in Levittown, according to a letter from School District Superintendent Todd Winch.

The letter says no weapons were involved in the incident and there was no threat to the school.

It said all students and staff are safe.

The superintendent says the incident was reported to Nassau County police.

A 15-year-old from Lindenhurst was also arrested after police say he threatened to shoot people at Brennan High School in West Babylon.