More than a dozen school districts across Texas have reported receiving threats in the wake of the Uvalde shooting.

Driving the news: Police have arrested several people for allegedly making terroristic threats to conduct shootings at public schools in the week since a gunman opened fire at an elementary school in South Texas, killing 19 children and two adults.

• In several cases, guns were found on campus. Many schools have gone into lockdown. At least one district ended the school year early after what it called "continued rumors of threats."

What they're saying: "Studies have shown that, generally, the copycat phenomenon lasts for … maybe two weeks," retired FBI special agent in charge Michael Tabman recently told Fox News.

What happened: Police in Richardson arrested a student after officials said he was allegedly seen walking to a high school with a rifle.

• Donna ISD, in South Texas, shut down all campuses Thursday and Friday after a threat was reported to police. An AK-47 and a list of targeted students were reportedly found by law enforcement officers in the home of one suspect.
• Rain ISD, in Emory, was locked down after officials were told about a threat made via social media. Authorities there reportedly seized a shotgun, ammunition and two pistols from one vehicle and another shotgun from a second vehicle.
• A high school student in Seguin was arrested after allegedly threatening to bring a weapon to campus .
• Four people were arrested in connection to a threat against Manor ISD schools , outside Austin. The police chief there reported that a video posted to social media depicted a young man with an assault rifle using foul language.
• A weapon was found at a San Antonio middle school after a parent reported that a student may have brought it to campus.
• A high school student in Houston was arrested after bringing an unloaded gun to school .
• Mercedes ISD, in the Rio Grande Valley, ended classes a week early after multiple rumors of threats and one student's arrest.

Meanwhile, a parent in Arlington with a concealed weapon dropped his gun and accidentally shot himself while at an elementary school.