The school is releasing students to parents if they wish to pick them up, Fort Bend ISD said. A pep rally scheduled for Friday has been canceled.
According to the district, campus administrators received a report on Friday regarding a student in possession of an airsoft gun.
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After the district received the report, campus police were notified and the student was identified, FBISD said.
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Officers were able to immediately confiscate the airsoft gun from the student, who was detained by FBISD officers.
The district said all applicable criminal charges are being pursued.
In an update on Twitter, the district said multiple physical altercations occurred at the school, but there was no active shooter and no shots were fired.
Law enforcement is on scene and the school is in a hold with students and staff inside their rooms and designated areas, FBISD tweeted.
The district said there were no reports of injuries and the students and staff are safe.
All parties responsible have been identified and face serious disciplinary action, FBISD said.
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The Hightower High School incident was just the latest in a string of threats keeping school officers busy this week.
On Tuesday, Houston ISD's Heights High School had a hoax call reporting an active shooter.
The false report resulted in lockdown and large police presence at the school.
Similar false calls were reported to more than a dozen other schools in Texas and California, officials said.
When asked if the false reports are connected, investigators in Waco said they "are not sure," but ABC13 sources said the calls in Texas came from the same number.
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In addition to Houston and Waco, ABC13 sources said false reports were also made in Pflugerville and a fourth Texas school district.
The following day, Aldine ISD's Eisenhower High School received social media threats.
Then on Thursday, Klein Forest High School students were forced to exit the campus after the district said a student typed on a district-issued device that he had a pipe bomb.
The message was flagged and school was canceled for the rest of the day as police searched through the building. No bomb was found.
RELATED: Additional police presence as classes resume at Klein Forest after student made bomb threat